backend/app/controllers/gekanator_games_controller.rb

@@ -20,4 +20,91 @@ class GekanatorGamesController < ApplicationController
       render json: { errors: game.errors.full_messages }, status: :unprocessable_entity
     end
   end
+
+  def extra_questions
+    return head :not_found unless current_user&.admin?
+
+    game = GekanatorGame.find_by(id: params[:id])
+    return head :not_found unless game
+
+    asked_ids = Array(game.answers).filter_map { |answer|
+      answer['questionId'] || answer[:questionId]
+    }
+    existing_example_ids =
+        GekanatorQuestionExample.where(post_id: game.correct_post_id)
+                                .select(:gekanator_question_id)
+    questions =
+        GekanatorQuestion
+        .accepted
+        .where(kind: 'post_similarity', source: 'user_suggested')
+        .where.not(id: existing_example_ids)
+        .order(priority_weight: :desc, id: :asc)
+
+    render json: {
+      questions: questions.filter_map { |question|
+        json = extra_question_json(question)
+        next if asked_ids.include?(json[:id].to_s)
+        next if asked_ids.include?("post-similarity:#{ json[:id] }")
+
+        json
+      }.first(2)
+    }
+  end
+
+  def extra_question_answers
+    return head :not_found unless current_user&.admin?
+
+    game = GekanatorGame.find_by(id: params[:id])
+    return head :not_found unless game
+
+    answer_params = params.require(:answers)
+    if !answer_params.is_a?(Array)
+      return render_validation_error fields: { answers: ['配列で指定してください．'] }
+    end
+
+    answers = answer_params.map { |answer|
+      {
+        question_id: answer.require(:question_id),
+        answer: answer.require(:answer)
+      }
+    }
+    questions = GekanatorQuestion.where(id: answers.map { _1[:question_id] })
+    question_by_id = questions.index_by(&:id)
+    if questions.length != answers.length
+      return render_validation_error fields: { answers: ['質問が見つかりません．'] }
+    end
+    if questions.any? { |question| question.status != 'accepted' || question.kind != 'post_similarity' }
+      return render_validation_error fields: { answers: ['質問が不正です．'] }
+    end
+
+    ActiveRecord::Base.transaction do
+      answers.each do |item|
+        question = question_by_id[item[:question_id]]
+        example =
+            GekanatorQuestionExample.find_or_initialize_by(
+                gekanator_question: question,
+                post: game.correct_post,
+                user: current_user)
+        example.assign_attributes(
+            gekanator_game: game,
+            answer: item[:answer],
+            source: 'post_game_extra',
+            weight: 1.0)
+        example.save!
+      end
+    end
+
+    render json: { count: answers.length }, status: :created
+  end
+
+  private
+
+  def extra_question_json question
+    {
+      id: question.id,
+      text: question.text,
+      source: question.source,
+      priority_weight: question.priority_weight
+    }
+  end
 end

backend/app/controllers/gekanator_question_suggestions_controller.rb

@@ -11,7 +11,14 @@ class GekanatorQuestionSuggestionsController < ApplicationController
         question_text: params.require(:question_text),
         answer: params.require(:answer))
 
-    if suggestion.save
+    if suggestion.valid?
+      ActiveRecord::Base.transaction do
+        suggestion.save!
+        Gekanator::QuestionSuggestionPromoter.call(
+            suggestion: suggestion,
+            user: current_user)
+      end
+
       render json: {
         id: suggestion.id,
         count: game.question_suggestions.count

backend/app/controllers/gekanator_questions_controller.rb

@@ -2,7 +2,11 @@ class GekanatorQuestionsController < ApplicationController
   def index
     return head :not_found unless current_user&.admin?
 
-    questions = GekanatorQuestion.accepted.order(priority_weight: :desc, id: :asc)
+    questions =
+        GekanatorQuestion
+        .accepted
+        .includes(:gekanator_question_examples)
+        .order(priority_weight: :desc, id: :asc)
 
     render json: {
       questions: questions.map { |question| question_json(question) }
@@ -12,7 +16,7 @@ class GekanatorQuestionsController < ApplicationController
   private
 
   def question_json question
-    {
+    json = {
       id: question_id_for(question),
       text: question.text,
       kind: question.kind,
@@ -20,6 +24,10 @@ class GekanatorQuestionsController < ApplicationController
       source: question.source,
       priority_weight: question.priority_weight
     }
+    if question.kind == 'post_similarity'
+      json[:example_answers] = example_answers_json(question)
+    end
+    json
   end
 
   def question_id_for question
@@ -40,6 +48,8 @@ class GekanatorQuestionsController < ApplicationController
       "title:length-greater-than:#{ condition[:length] }"
     when 'title-has-ascii'
       'title:ascii'
+    when 'post-similarity'
+      "post-similarity:#{ question.id }"
     else
       "catalog:#{ question.id }"
     end
@@ -54,4 +64,20 @@ class GekanatorQuestionsController < ApplicationController
 
     json
   end
+
+  def example_answers_json question
+    question
+        .gekanator_question_examples
+        .group_by(&:post_id)
+        .transform_values { |examples| aggregate_answer(examples) }
+  end
+
+  def aggregate_answer examples
+    examples
+        .group_by(&:answer)
+        .map { |answer, grouped| [answer, grouped.sum(&:weight), grouped.max_by(&:updated_at)&.updated_at] }
+        .sort_by { |(_answer, weight, updated_at)| [-weight, -(updated_at&.to_f || 0)] }
+        .first
+        &.first
+  end
 end

backend/app/models/gekanator_game.rb

@@ -5,6 +5,9 @@ class GekanatorGame < ApplicationRecord
   has_many :question_suggestions,
            class_name: 'GekanatorQuestionSuggestion',
            dependent: :delete_all
+  has_many :question_examples,
+           class_name: 'GekanatorQuestionExample',
+           dependent: :delete_all
 
   validates :answers, presence: true
   validates :question_count, numericality: { greater_than_or_equal_to: 0 }

backend/app/models/gekanator_question.rb

@@ -1,10 +1,11 @@
 class GekanatorQuestion < ApplicationRecord
-  KINDS = ['tag', 'source', 'title', 'original_date'].freeze
+  KINDS = ['tag', 'source', 'title', 'original_date', 'post_similarity'].freeze
   SOURCES = ['user_suggested', 'ai_generated', 'admin_curated'].freeze
-  STATUSES = ['pending', 'accepted', 'rejected'].freeze
+  STATUSES = ['pending', 'accepted', 'rejected', 'disabled'].freeze
 
   belongs_to :gekanator_question_suggestion, optional: true
   belongs_to :created_by, class_name: 'User', optional: true
+  has_many :gekanator_question_examples, dependent: :delete_all
 
   validates :kind, presence: true, inclusion: { in: KINDS }
   validates :source, presence: true, inclusion: { in: SOURCES }

backend/app/models/gekanator_question_example.rb

@@ -0,0 +1,17 @@
+class GekanatorQuestionExample < ApplicationRecord
+  ANSWERS = GekanatorQuestionSuggestion::ANSWERS
+  SOURCES = ['initial_suggestion', 'post_game_extra'].freeze
+
+  belongs_to :gekanator_question
+  belongs_to :post
+  belongs_to :user
+  belongs_to :gekanator_game, optional: true
+
+  validates :answer, presence: true, inclusion: { in: ANSWERS }
+  validates :source, presence: true, inclusion: { in: SOURCES }
+  validates :weight,
+            presence: true,
+            numericality: {
+              greater_than: 0
+            }
+end

backend/app/models/post.rb

@@ -21,6 +21,7 @@ class Post < ApplicationRecord
            foreign_key: :correct_post_id,
            dependent: :delete_all,
            inverse_of: :correct_post
+  has_many :gekanator_question_examples, dependent: :delete_all
 
   has_many :parent_post_implications,
            class_name: 'PostImplication',

backend/app/services/gekanator/question_suggestion_promoter.rb

@@ -0,0 +1,48 @@
+module Gekanator
+  class QuestionSuggestionPromoter
+    def self.call(...) = new(...).call
+
+    def initialize suggestion:, user:
+      @suggestion = suggestion
+      @user = user
+    end
+
+    def call
+      suggestion.with_lock do
+        return promoted_question if suggestion.processed?
+
+        question = GekanatorQuestion.create!(
+            text: suggestion.question_text,
+            kind: 'post_similarity',
+            source: 'user_suggested',
+            status: 'accepted',
+            priority_weight: 1.2,
+            condition: {
+              type: 'post-similarity',
+              postId: suggestion.gekanator_game.correct_post_id,
+              answer: suggestion.answer,
+              threshold: 0.65
+            },
+            gekanator_question_suggestion: suggestion,
+            created_by: user)
+        GekanatorQuestionExample.create!(
+            gekanator_question: question,
+            post: suggestion.gekanator_game.correct_post,
+            user: user,
+            gekanator_game: suggestion.gekanator_game,
+            answer: suggestion.answer,
+            source: 'initial_suggestion')
+        suggestion.update!(processed: true)
+        question
+      end
+    end
+
+    private
+
+    attr_reader :suggestion, :user
+
+    def promoted_question
+      suggestion.gekanator_questions.order(id: :desc).first
+    end
+  end
+end

backend/config/routes.rb

@@ -64,7 +64,12 @@ Rails.application.routes.draw do
   end
 
   namespace :gekanator do
-    resources :games, only: [:create], controller: '/gekanator_games'
+    resources :games, only: [:create], controller: '/gekanator_games' do
+      member do
+        get :extra_questions
+        post :extra_question_answers
+      end
+    end
     resources :posts, only: [:index], controller: '/gekanator_posts'
     resources :questions, only: [:index], controller: '/gekanator_questions'
     resources :question_suggestions,

backend/db/migrate/20260610000000_create_gekanator_question_examples.rb

@@ -0,0 +1,19 @@
+class CreateGekanatorQuestionExamples < ActiveRecord::Migration[8.0]
+  def change
+    create_table :gekanator_question_examples do |t|
+      t.references :gekanator_question, null: false, foreign_key: true
+      t.references :post, null: false, foreign_key: true
+      t.references :user, null: false, foreign_key: true
+      t.references :gekanator_game, null: true, foreign_key: true
+      t.string :answer, null: false
+      t.string :source, null: false, default: 'post_game_extra'
+      t.float :weight, null: false, default: 1.0
+      t.timestamps
+    end
+
+    add_index :gekanator_question_examples,
+              [:gekanator_question_id, :post_id, :user_id],
+              unique: true,
+              name: 'idx_gekanator_question_examples_on_question_post_user'
+  end
+end

backend/db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[8.0].define(version: 2026_06_09_001000) do
+ActiveRecord::Schema[8.0].define(version: 2026_06_10_000000) do
   create_table "active_storage_attachments", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.string "name", null: false
     t.string "record_type", null: false
@@ -75,6 +75,23 @@ ActiveRecord::Schema[8.0].define(version: 2026_06_09_001000) do
     t.check_constraint "`question_count` >= 0", name: "chk_gekanator_games_question_count_nonnegative"
   end
 
+  create_table "gekanator_question_examples", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+    t.bigint "gekanator_question_id", null: false
+    t.bigint "post_id", null: false
+    t.bigint "user_id", null: false
+    t.bigint "gekanator_game_id"
+    t.string "answer", null: false
+    t.string "source", default: "post_game_extra", null: false
+    t.float "weight", default: 1.0, null: false
+    t.datetime "created_at", null: false
+    t.datetime "updated_at", null: false
+    t.index ["gekanator_game_id"], name: "index_gekanator_question_examples_on_gekanator_game_id"
+    t.index ["gekanator_question_id", "post_id", "user_id"], name: "idx_gekanator_question_examples_on_question_post_user", unique: true
+    t.index ["gekanator_question_id"], name: "index_gekanator_question_examples_on_gekanator_question_id"
+    t.index ["post_id"], name: "index_gekanator_question_examples_on_post_id"
+    t.index ["user_id"], name: "index_gekanator_question_examples_on_user_id"
+  end
+
   create_table "gekanator_question_suggestions", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.bigint "gekanator_game_id", null: false
     t.bigint "user_id", null: false
@@ -553,6 +570,10 @@ ActiveRecord::Schema[8.0].define(version: 2026_06_09_001000) do
   add_foreign_key "gekanator_games", "posts", column: "correct_post_id"
   add_foreign_key "gekanator_games", "posts", column: "guessed_post_id"
   add_foreign_key "gekanator_games", "users"
+  add_foreign_key "gekanator_question_examples", "gekanator_games"
+  add_foreign_key "gekanator_question_examples", "gekanator_questions"
+  add_foreign_key "gekanator_question_examples", "posts"
+  add_foreign_key "gekanator_question_examples", "users"
   add_foreign_key "gekanator_question_suggestions", "gekanator_games", on_delete: :cascade
   add_foreign_key "gekanator_question_suggestions", "users"
   add_foreign_key "gekanator_questions", "gekanator_question_suggestions"

frontend/src/lib/gekanator.ts

@@ -21,6 +21,7 @@ export type GekanatorQuestionKind =
     | 'source'
     | 'title'
     | 'original_date'
+    | 'post_similarity'
 
 export type GekanatorQuestionSource =
     | 'default'
@@ -36,6 +37,18 @@ export type GekanatorQuestionCondition =
     | { type: 'original-month-day'; monthDay: string }
     | { type: 'title-length-greater-than'; length: number }
     | { type: 'title-has-ascii' }
+    | {
+	  type: 'post-similarity'
+	  postId: number
+	  answer: GekanatorAnswerValue
+	  threshold: number
+      }
+
+export type GekanatorExtraQuestion = {
+    id:              number
+    text:            string
+    source:          GekanatorQuestionSource
+    priorityWeight:  number }
 
 export type StoredGekanatorQuestion = {
     id:              string
@@ -43,7 +56,8 @@ export type StoredGekanatorQuestion = {
     kind:            GekanatorQuestionKind
     condition:       GekanatorQuestionCondition
     source?:         GekanatorQuestionSource
-    priorityWeight?: number }
+    priorityWeight?: number
+    exampleAnswers?: Record<`${ number }`, GekanatorAnswerValue> }
 
 export type GekanatorQuestion = {
     id:              string
@@ -52,8 +66,24 @@ export type GekanatorQuestion = {
     condition:       GekanatorQuestionCondition
     source:          GekanatorQuestionSource
     priorityWeight:  number
+    exampleAnswers?: Record<`${ number }`, GekanatorAnswerValue>
     test:            (post: Post) => boolean }
 
+
+const directExampleAnswerFor = (
+    question:  StoredGekanatorQuestion,
+    post:      Post,
+): GekanatorAnswerValue | null => {
+  const direct = question.exampleAnswers?.[String (post.id) as `${ number }`]
+  if (direct)
+    return direct
+
+  if (question.condition.type === 'post-similarity' && question.condition.postId === post.id)
+    return question.condition.answer
+
+  return null
+}
+
 const countBy = <T extends string | number> (values: T[]): Map<T, number> => {
   const counts = new Map<T, number> ()
   values.forEach (value => counts.set (value, (counts.get (value) ?? 0) + 1))
@@ -172,24 +202,59 @@ const questionableTag = (post: Post, key: string): boolean => {
 
 const questionMatches = (
     post:       Post,
-    condition:  GekanatorQuestionCondition,
+    question:   StoredGekanatorQuestion,
 ): boolean => {
-  switch (condition.type)
+  const directAnswer = directExampleAnswerFor (question, post)
+  if (directAnswer)
+    return question.condition.type === 'post-similarity'
+	? directAnswer === question.condition.answer
+	: directAnswer === 'yes'
+
+  switch (question.condition.type)
   {
   case 'tag':
-    return questionableTag (post, condition.key)
+    return questionableTag (post, question.condition.key)
   case 'source':
-    return hostOf (post) === condition.host
+    return hostOf (post) === question.condition.host
   case 'original-year':
-    return originalYearOf (post) === condition.year
+    return originalYearOf (post) === question.condition.year
   case 'original-month':
-    return originalMonthOf (post) === condition.month
+    return originalMonthOf (post) === question.condition.month
   case 'original-month-day':
-    return originalMonthDayOf (post) === condition.monthDay
+    return originalMonthDayOf (post) === question.condition.monthDay
   case 'title-length-greater-than':
-    return (post.title?.length ?? 0) > condition.length
+    return (post.title?.length ?? 0) > question.condition.length
   case 'title-has-ascii':
     return /[A-Za-z0-9]/.test (post.title ?? '')
+  case 'post-similarity':
+    return false
+  }
+}
+
+
+export const expectedAnswerForQuestion = (
+    question:  StoredGekanatorQuestion | GekanatorQuestion | undefined,
+    post:      Post | null,
+): GekanatorAnswerValue | null => {
+  if (!(question) || !(post))
+    return null
+
+  const directAnswer = directExampleAnswerFor (question, post)
+  if (directAnswer)
+    return directAnswer
+
+  switch (question.condition.type)
+  {
+  case 'tag':
+  case 'source':
+  case 'original-year':
+  case 'original-month':
+  case 'original-month-day':
+  case 'title-length-greater-than':
+  case 'title-has-ascii':
+    return questionMatches (post, question) ? 'yes' : 'no'
+  case 'post-similarity':
+    return null
   }
 }
 
@@ -200,7 +265,7 @@ export const restoreGekanatorQuestion = (
   ...question,
   source: question.source ?? 'default',
   priorityWeight: question.priorityWeight ?? 1,
-  test: (post: Post) => questionMatches (post, question.condition) })
+  test: (post: Post) => questionMatches (post, question) })
 
 
 export const storeGekanatorQuestion = (
@@ -211,7 +276,8 @@ export const storeGekanatorQuestion = (
   kind: question.kind,
   condition: question.condition,
   source: question.source,
-  priorityWeight: question.priorityWeight })
+  priorityWeight: question.priorityWeight,
+  exampleAnswers: question.exampleAnswers })
 
 
 export const fetchGekanatorPosts = async (): Promise<Post[]> => {
@@ -226,6 +292,15 @@ export const fetchGekanatorQuestions = async (): Promise<StoredGekanatorQuestion
 }
 
 
+export const fetchGekanatorExtraQuestions = async (
+    gameId: number,
+): Promise<GekanatorExtraQuestion[]> => {
+  const data = await apiGet<{ questions: GekanatorExtraQuestion[] }> (
+      `/gekanator/games/${ gameId }/extra_questions`)
+  return data.questions
+}
+
+
 export const buildGekanatorQuestions = (posts: Post[]): GekanatorQuestion[] => {
   const tagCounts = countBy (posts.flatMap (post =>
       post.tags
@@ -393,3 +468,16 @@ export const saveGekanatorQuestionSuggestion = async ({
 	gekanator_game_id: gekanatorGameId,
 	question_text: questionText,
 	answer })
+
+
+export const saveGekanatorExtraQuestionAnswers = async ({
+    gameId,
+    answers,
+}: {
+    gameId:   number
+    answers:  { questionId: number; answer: GekanatorAnswerValue }[]
+}) =>
+    await apiPost (`/gekanator/games/${ gameId }/extra_question_answers`, {
+	answers: answers.map (item => ({
+	    question_id: item.questionId,
+	    answer: item.answer })) })

frontend/src/lib/queryKeys.ts

@@ -11,7 +11,9 @@ export const postsKeys = {
 export const gekanatorKeys = {
     root:      ['gekanator'] as const,
     posts:     () => ['gekanator', 'posts'] as const,
-    questions: () => ['gekanator', 'questions'] as const }
+    questions: () => ['gekanator', 'questions'] as const,
+    extraQuestions: (gameId: number) =>
+		       ['gekanator', 'games', gameId, 'extra-questions'] as const }
 
 export const tagsKeys = {
     root:         ['tags'] as const,

frontend/src/pages/GekanatorPage.tsx

@@ -1,4 +1,4 @@
-import { useMutation, useQuery } from '@tanstack/react-query'
+import { useMutation, useQuery, useQueryClient } from '@tanstack/react-query'
 import { useEffect, useMemo, useState } from 'react'
 import { Helmet } from 'react-helmet-async'
 
@@ -6,9 +6,12 @@ import PrefetchLink from '@/components/PrefetchLink'
 import MainArea from '@/components/layout/MainArea'
 import { SITE_TITLE } from '@/config'
 import { buildGekanatorQuestions,
+	 expectedAnswerForQuestion,
+	 fetchGekanatorExtraQuestions,
 	 fetchGekanatorQuestions,
 	 fetchGekanatorPosts,
 	 restoreGekanatorQuestion,
+	 saveGekanatorExtraQuestionAnswers,
 	 saveGekanatorGame,
 	 saveGekanatorQuestionSuggestion,
 	 storeGekanatorQuestion } from '@/lib/gekanator'
@@ -19,6 +22,7 @@ import type { FC } from 'react'
 
 import type { GekanatorAnswerLog,
 	      GekanatorAnswerValue,
+	      GekanatorExtraQuestion,
 	      GekanatorQuestion,
 	      StoredGekanatorQuestion } from '@/lib/gekanator'
 import type { Post } from '@/types'
@@ -31,6 +35,7 @@ type Phase =
     | 'end'
     | 'review'
     | 'question_suggestion'
+    | 'extra_questions'
     | 'learned'
 
 type AnswerOption = {
@@ -87,7 +92,10 @@ type StoredGekanatorGame = {
     gameSeed?:                   string
     questionSuggestion:          string
     questionSuggestionAnswer:    GekanatorAnswerValue
-    questionSuggestionCount?:    number }
+    questionSuggestionCount?:    number
+    extraQuestions?:             GekanatorExtraQuestion[]
+    extraQuestionAnswers?:       Record<string, GekanatorAnswerValue>
+    extraQuestionState?:         'idle' | 'loading' | 'ready' | 'empty' | 'saved' }
 
 const answerOptions: AnswerOption[] = [
     { label: 'はい', value: 'yes' },
@@ -219,6 +227,16 @@ const loadStoredGame = (): StoredGekanatorGame | null => {
 const isStoredPhase = (phase: Phase): boolean => phase !== 'intro'
 
 
+const resettableExtraQuestionState = (): {
+    extraQuestions:        GekanatorExtraQuestion[]
+    extraQuestionAnswers:  Record<string, GekanatorAnswerValue>
+    extraQuestionState:    'idle'
+} => ({
+  extraQuestions: [],
+  extraQuestionAnswers: { },
+  extraQuestionState: 'idle' })
+
+
 const deltaFor = (matched: boolean, answer: GekanatorAnswerValue): number => {
   switch (answer)
   {
@@ -236,6 +254,55 @@ const deltaFor = (matched: boolean, answer: GekanatorAnswerValue): number => {
 }
 
 
+const answerScalarFor = (
+    answer:  GekanatorAnswerValue | null,
+): number | null => {
+  switch (answer)
+  {
+  case 'yes':
+    return 1
+  case 'partial':
+    return .5
+  case 'probably_no':
+    return -.5
+  case 'no':
+    return -1
+  case 'unknown':
+  case null:
+    return null
+  }
+}
+
+
+const deltaForExpectedAnswer = (
+    expected:  GekanatorAnswerValue | null,
+    answer:    GekanatorAnswerValue,
+): number => {
+  if (answer === 'unknown' || expected === null || expected === 'unknown')
+    return 0
+
+  if (expected === 'yes' || expected === 'no')
+    return deltaFor (expected === 'yes', answer)
+
+  const expectedScalar = answerScalarFor (expected)
+  const answerScalar = answerScalarFor (answer)
+  if (expectedScalar === null || answerScalar === null)
+    return 0
+
+  const distance = Math.abs (expectedScalar - answerScalar)
+  if (distance >= 2)
+    return -4
+  if (distance >= 1.5)
+    return -2
+  if (distance >= 1)
+    return 0
+  if (distance >= .5)
+    return 2
+
+  return 4
+}
+
+
 const answerWeightFor = (
     questionId:           string,
     softenedQuestionIds:  Set<string>,
@@ -277,10 +344,11 @@ const recalculateScores = ({
 
     const weight = answerWeightFor (answer.questionId, softenedQuestionIds)
     posts.forEach (post => {
+      const expected = expectedAnswerForQuestion (question, post)
       nextScores.set (
 	  post.id,
 	  (nextScores.get (post.id) ?? 0)
-	      + deltaFor (question.test (post), answer.answer) * weight)
+	      + deltaForExpectedAnswer (expected, answer.answer) * weight)
     })
   })
 
@@ -318,9 +386,10 @@ const candidatePostsFor = ({
       switch (answer.answer)
       {
       case 'yes':
-	return question.test (post)
+      case 'no': {
-      case 'no':
+	const expected = expectedAnswerForQuestion (question, post)
-	return !(question.test (post))
+	return expected === null || expected === 'unknown' || expected === answer.answer
+      }
       default:
 	return true
       }
@@ -378,20 +447,19 @@ const previewAnswer = ({
     answer:    GekanatorAnswerValue
 }): AnswerPreview => {
   const hardFilteredPosts =
-      answer === 'yes'
+      answer === 'unknown'
-	? posts.filter (post => question.test (post))
+	? posts
-	: answer === 'no'
+	: posts.filter (post => expectedAnswerForQuestion (question, post) === answer)
-	  ? posts.filter (post => !(question.test (post)))
-	  : posts
   const nextPosts =
-      (answer === 'yes' || answer === 'no') && hardFilteredPosts.length > 0
+      answer !== 'unknown' && hardFilteredPosts.length > 0
 	? hardFilteredPosts
 	: posts
   const nextScores = new Map (scores)
   nextPosts.forEach (post => {
+    const expected = expectedAnswerForQuestion (question, post)
     nextScores.set (
 	post.id,
-	(nextScores.get (post.id) ?? 0) + deltaFor (question.test (post), answer))
+	(nextScores.get (post.id) ?? 0) + deltaForExpectedAnswer (expected, answer))
   })
 
   const confidences = confidencesFor (nextPosts, nextScores)
@@ -497,6 +565,8 @@ const sameConditionValue = (
       return String (condition.length)
     case 'title-has-ascii':
       return ''
+    case 'post-similarity':
+      return `${ condition.postId }:${ condition.answer }:${ condition.threshold }`
     }
   }
 
@@ -757,16 +827,13 @@ const PostMiniCard: FC<{ post: Post }> = ({ post }) => (
 const expectedAnswerFor = (
     question:     GekanatorQuestion | undefined,
     correctPost:  Post | null,
-): GekanatorAnswerValue | null => {
+): GekanatorAnswerValue | null =>
-  if (!(question) || !(correctPost))
+    expectedAnswerForQuestion (question, correctPost)
-    return null
-
-  return question.test (correctPost) ? 'yes' : 'no'
-}
 
 
 const GekanatorPage: FC = () => {
   const storedGame = useMemo (loadStoredGame, [])
+  const queryClient = useQueryClient ()
   const [gameSeed, setGameSeed] = useState (
       storedGame?.gameSeed ?? createGameSeed ())
   const [phase, setPhase] = useState<Phase> (storedGame?.phase ?? 'intro')
@@ -810,6 +877,14 @@ const GekanatorPage: FC = () => {
       useState<GekanatorAnswerValue> (storedGame?.questionSuggestionAnswer ?? 'yes')
   const [questionSuggestionCount, setQuestionSuggestionCount] = useState (
       storedGame?.questionSuggestionCount ?? 0)
+  const [extraQuestions, setExtraQuestions] = useState<GekanatorExtraQuestion[]> (
+      storedGame?.extraQuestions ?? [])
+  const [extraQuestionAnswers, setExtraQuestionAnswers] =
+      useState<Record<string, GekanatorAnswerValue>> (
+	  storedGame?.extraQuestionAnswers ?? { })
+  const [extraQuestionState, setExtraQuestionState] = useState<
+      'idle' | 'loading' | 'ready' | 'empty' | 'saved'
+  > (storedGame?.extraQuestionState ?? 'idle')
   const [history, setHistory] = useState<GameSnapshot[]> ([])
 
   const { data: posts = [], isLoading, error } = useQuery ({
@@ -876,7 +951,10 @@ const GekanatorPage: FC = () => {
 	gameSeed,
 	questionSuggestion,
 	questionSuggestionAnswer,
-	questionSuggestionCount }
+	questionSuggestionCount,
+	extraQuestions,
+	extraQuestionAnswers,
+	extraQuestionState }
 
     try
     {
@@ -908,7 +986,10 @@ const GekanatorPage: FC = () => {
       gameSeed,
       questionSuggestion,
       questionSuggestionAnswer,
-      questionSuggestionCount])
+      questionSuggestionCount,
+      extraQuestions,
+      extraQuestionAnswers,
+      extraQuestionState])
 
   const eligiblePosts = useMemo (
       () => candidatePostsFor ({
@@ -985,10 +1066,25 @@ const GekanatorPage: FC = () => {
 	setQuestionSuggestion ('')
 	setQuestionSuggestionAnswer ('yes')
       }})
+  const extraQuestionAnswersMutation = useMutation ({
+      mutationFn: saveGekanatorExtraQuestionAnswers,
+      onSuccess: () => {
+	setExtraQuestionState ('saved')
+	setPhase ('learned')
+      }})
+
+  const resetExtraQuestionState = () => {
+    const next = resettableExtraQuestionState ()
+    setExtraQuestions (next.extraQuestions)
+    setExtraQuestionAnswers (next.extraQuestionAnswers)
+    setExtraQuestionState (next.extraQuestionState)
+    extraQuestionAnswersMutation.reset ()
+  }
 
   const reset = () => {
     clearStoredGame ()
     saveMutation.reset ()
+    questionSuggestionMutation.reset ()
     setPhase ('intro')
     setScores (new Map ())
     setAnswers ([])
@@ -1010,6 +1106,7 @@ const GekanatorPage: FC = () => {
     setQuestionSuggestion ('')
     setQuestionSuggestionAnswer ('yes')
     setQuestionSuggestionCount (0)
+    resetExtraQuestionState ()
     setHistory ([])
   }
 
@@ -1188,6 +1285,7 @@ const GekanatorPage: FC = () => {
 
     saveMutation.reset ()
     questionSuggestionMutation.reset ()
+    resetExtraQuestionState ()
     setSaved (false)
     setSavedGameId (null)
     setReviewGuessedPostId (guessedPostId)
@@ -1203,6 +1301,7 @@ const GekanatorPage: FC = () => {
 
     saveMutation.reset ()
     questionSuggestionMutation.reset ()
+    resetExtraQuestionState ()
     setSaved (false)
     setSavedGameId (null)
     setSelectingCorrectPost (false)
@@ -1236,6 +1335,7 @@ const GekanatorPage: FC = () => {
   }
 
   const saveAndLearn = () => {
+    resetExtraQuestionState ()
     saveReviewedResult (() => setPhase ('learned'))
   }
 
@@ -1344,6 +1444,7 @@ const GekanatorPage: FC = () => {
   const correctAnswerAt = (index: number, value: GekanatorAnswerValue) => {
     setSaved (false)
     setSavedGameId (null)
+    resetExtraQuestionState ()
     setAnswers (answers.map ((answer, i) =>
 	i === index ? { ...answer, answer: value } : answer))
   }
@@ -1353,6 +1454,7 @@ const GekanatorPage: FC = () => {
       {
 	setSaved (false)
 	setSavedGameId (null)
+	resetExtraQuestionState ()
 	setReviewCorrectPostId (post.id)
 	setSelectingCorrectPost (false)
 	setSearch ('')
@@ -1383,6 +1485,60 @@ const GekanatorPage: FC = () => {
       })
       .slice (0, 20)
 
+  const loadExtraQuestions = async (gameId: number) => {
+    extraQuestionAnswersMutation.reset ()
+    setExtraQuestionState ('loading')
+    setExtraQuestions ([])
+    setExtraQuestionAnswers ({ })
+    setPhase ('extra_questions')
+
+    try
+    {
+      const questions = await queryClient.fetchQuery ({
+	  queryKey: gekanatorKeys.extraQuestions (gameId),
+	  queryFn: () => fetchGekanatorExtraQuestions (gameId) })
+      setExtraQuestions (questions)
+      setExtraQuestionState (questions.length > 0 ? 'ready' : 'empty')
+    }
+    catch
+    {
+      setExtraQuestionState ('empty')
+    }
+  }
+
+  const startExtraQuestions = () => {
+    if (reviewCorrectPostId === null || saveMutation.isPending)
+      return
+
+    saveReviewedResult (gameId => {
+      void loadExtraQuestions (gameId)
+    })
+  }
+
+  const answerExtraQuestion = (
+      questionId:  number,
+      value:       GekanatorAnswerValue,
+  ) => {
+    setExtraQuestionAnswers ({
+	...extraQuestionAnswers,
+	[String (questionId)]: value })
+  }
+
+  const saveExtraQuestions = () => {
+    if (
+	savedGameId === null
+	|| extraQuestionAnswersMutation.isPending
+	|| extraQuestions.some (question => !(extraQuestionAnswers[String (question.id)]))
+    )
+      return
+
+    extraQuestionAnswersMutation.mutate ({
+	gameId: savedGameId,
+	answers: extraQuestions.map (question => ({
+	    questionId: question.id,
+	    answer: extraQuestionAnswers[String (question.id)] })) })
+  }
+
   const dialogue =
       phase === 'learned' && resultWon
 	? <>グカカカカwwwww  <ruby>洗澡鹿<rt>シーザオグカ</rt></ruby>は何でもお見通し!</>
@@ -1650,6 +1806,18 @@ const GekanatorPage: FC = () => {
 			    onClick={() => setPhase ('question_suggestion')}>
 			  質問を追加
 			</button>
+			<button
+			    type="button"
+			    className="rounded border border-yellow-300 px-4 py-2
+				       hover:bg-yellow-100 dark:border-red-700
+				       dark:hover:bg-red-900 disabled:opacity-50"
+			    disabled={reviewCorrectPostId === null
+				      || saveMutation.isPending
+				      || extraQuestionState === 'loading'
+				      || extraQuestionAnswersMutation.isPending}
+			    onClick={startExtraQuestions}>
+			  追加で質問に答へる
+			</button>
 		      </div>
 		    </div>)}
 
@@ -1843,9 +2011,81 @@ const GekanatorPage: FC = () => {
 			  </p>)}
 		    </div>)}
 
+		{phase === 'extra_questions' && (
+		    <div className="space-y-4">
+		      <div>
+			<p className="text-sm text-neutral-500">追加学習</p>
+			<p className="text-xl font-bold">追加で 2 問まで答へてください。</p>
+		      </div>
+
+		      {extraQuestionState === 'loading' && (
+			  <p>追加質問を読み込んでゐます...</p>)}
+
+		      {extraQuestionState === 'empty' && (
+			  <p>追加で学習できる質問はありませんでした。</p>)}
+
+		      {extraQuestionState === 'ready' && (
+			  <div className="space-y-3">
+			    {extraQuestions.map ((question, index) => (
+				<div
+				    key={question.id}
+				    className="rounded border border-yellow-100 p-3
+					       dark:border-red-900">
+				  <div className="text-sm text-neutral-600 dark:text-neutral-300">
+				    追加質問 {index + 1}
+				  </div>
+				  <div className="font-bold">{question.text}</div>
+				  <div className="mt-3 flex flex-wrap gap-2">
+				    {answerOptions.map (option => (
+					<button
+					    key={option.value}
+					    type="button"
+					    className={cn (
+						'rounded border px-3 py-2',
+						extraQuestionAnswers[String (question.id)] === option.value
+						  ? 'border-pink-600 bg-pink-600 text-white'
+						  : 'border-yellow-300 hover:bg-yellow-100 dark:border-red-700 dark:hover:bg-red-900')}
+					    onClick={() => answerExtraQuestion (question.id, option.value)}>
+					  {option.label}
+					</button>))}
+				  </div>
+				</div>))}
+			  </div>)}
+
+		      {extraQuestionAnswersMutation.isError && (
+			  <p className="text-sm text-red-600">
+			    学習内容を保存できませんでした。通信状態を確認してもう一度試して。
+			  </p>)}
+
+		      <div className="flex flex-wrap gap-2">
+			<button
+			    type="button"
+			    className="rounded border border-neutral-300 px-4 py-2
+				       hover:bg-neutral-100 dark:border-neutral-700
+				       dark:hover:bg-red-900"
+			    disabled={extraQuestionAnswersMutation.isPending}
+			    onClick={() => setPhase ('end')}>
+			  戻る
+			</button>
+			<button
+			    type="button"
+			    className="rounded bg-pink-600 px-4 py-2 font-bold text-white
+				       hover:bg-pink-500 disabled:opacity-50"
+			    disabled={
+			      extraQuestionState !== 'ready'
+			      || extraQuestionAnswersMutation.isPending
+			      || extraQuestions.some (
+				  question => !(extraQuestionAnswers[String (question.id)]))
+			    }
+			    onClick={saveExtraQuestions}>
+			  学習する
+			</button>
+		      </div>
+		    </div>)}
+
 		{phase === 'learned' && (
 		    <div className="space-y-3">
-		      <p>覚えたよ．次はもっと見通す．</p>
+		      <p>{extraQuestionState === 'saved' ? '学習しました。' : '覚えたよ．次はもっと見通す．'}</p>
 		      <button
 			  type="button"
 			  className="rounded bg-pink-600 px-4 py-2 font-bold text-white