diff --git a/backend/app/controllers/deerjikists_controller.rb b/backend/app/controllers/deerjikists_controller.rb
new file mode 100644
index 0000000..b04eaf6
--- /dev/null
+++ b/backend/app/controllers/deerjikists_controller.rb
@@ -0,0 +1,47 @@
+class DeerjikistsController < ApplicationController
+  def show
+    platform = params[:platform].to_s.strip
+    code = params[:code].to_s.strip
+    return head :bad_request if platform.blank? || code.blank?
+
+    deerjikist = Deerjikist
+                 .joins(:tag)
+                 .includes(tag: :tag_name)
+                 .find_by(platform:, code:)
+    if deerjikist
+      render json: DeerjikistRepr.base(deerjikist)
+    else
+      head :not_found
+    end
+  end
+
+  def update
+    return head :unauthorized unless current_user
+    return head :forbidden unless current_user.member?
+
+    platform = params[:platform].to_s.strip
+    code = params[:code].to_s.strip
+    tag_id = params[:tag_id].to_i
+    return head :bad_request if platform.blank? || code.blank? || tag_id <= 0
+
+    deerjikist = Deerjikist.find_or_initialize_by(platform:, code:).tap do |d|
+      d.tag_id = tag_id
+      d.save!
+    end
+
+    render json: DeerjikistRepr.base(deerjikist)
+  end
+
+  def destroy
+    return head :unauthorized unless current_user
+    return head :forbidden unless current_user.member?
+
+    platform = params[:platform].to_s.strip
+    code = params[:code].to_s.strip
+    return head :bad_request if platform.blank? || code.blank?
+
+    Deerjikist.find([platform, code]).destroy!
+
+    head :no_content
+  end
+end
diff --git a/backend/app/controllers/tags_controller.rb b/backend/app/controllers/tags_controller.rb
index c4d5b0d..186b6b9 100644
--- a/backend/app/controllers/tags_controller.rb
+++ b/backend/app/controllers/tags_controller.rb
@@ -86,6 +86,27 @@ class TagsController < ApplicationController
     end
   end
 
+  def deerjikists
+    tag = Tag.joins(:tag_name)
+             .includes(:tag_name, tag_name: :wiki_page)
+             .find_by(id: params[:id])
+    return head :not_found unless tag
+
+    render json: DeerjikistRepr.many(tag.deerjikists)
+  end
+
+  def deerjikists_by_name
+    name = params[:name].to_s.strip
+    return head :bad_request if name.blank?
+
+    tag = Tag.joins(:tag_name)
+             .includes(:tag_name, tag_name: :wiki_page)
+             .find_by(tag_names: { name: })
+    return head :not_found unless tag
+
+    render json: DeerjikistRepr.many(tag.deerjikists)
+  end
+
   def update
     return head :unauthorized unless current_user
     return head :forbidden unless current_user.member?
diff --git a/backend/app/models/deerjikist.rb b/backend/app/models/deerjikist.rb
new file mode 100644
index 0000000..8447ef4
--- /dev/null
+++ b/backend/app/models/deerjikist.rb
@@ -0,0 +1,21 @@
+class Deerjikist < ApplicationRecord
+  self.primary_key = :platform, :code
+
+  belongs_to :tag
+
+  validates :platform, presence: true
+  validates :code, presence: true
+  validates :tag_id, presence: true
+
+  validate :tag_must_be_deerjikist
+
+  enum :platform, nico: 'nico', youtube: 'youtube'
+
+  private
+
+  def tag_must_be_deerjikist
+    if tag && !(tag.deerjikist?)
+      errors.add :tag, 'タグはニジラー・カテゴリである必要があります．'
+    end
+  end
+end
diff --git a/backend/app/models/tag.rb b/backend/app/models/tag.rb
index fa66f5c..83afbd3 100644
--- a/backend/app/models/tag.rb
+++ b/backend/app/models/tag.rb
@@ -24,6 +24,8 @@ class Tag < ApplicationRecord
 
   has_many :tag_similarities, dependent: :delete_all
 
+  has_many :deerjikists, dependent: :delete_all
+
   belongs_to :tag_name
   delegate :wiki_page, to: :tag_name
 
@@ -42,6 +44,7 @@ class Tag < ApplicationRecord
 
   validate :nico_tag_name_must_start_with_nico
   validate :tag_name_must_be_canonical
+  validate :category_must_be_deerjikist_with_deerjikists
 
   scope :nico_tags, -> { where(category: :nico) }
 
@@ -154,4 +157,10 @@ class Tag < ApplicationRecord
       errors.add :tag_name, 'tag_names へは実体を示す必要があります．'
     end
   end
+
+  def category_must_be_deerjikist_with_deerjikists
+    if !(deerjikist?) && deerjikists.exists?
+      errors.add :category, 'ニジラーと紐づいてゐるタグはニジラー・カテゴリである必要があります．'
+    end
+  end
 end
diff --git a/backend/app/representations/deerjikist_repr.rb b/backend/app/representations/deerjikist_repr.rb
new file mode 100644
index 0000000..fbb73c9
--- /dev/null
+++ b/backend/app/representations/deerjikist_repr.rb
@@ -0,0 +1,16 @@
+# frozen_string_literal: true
+
+
+module DeerjikistRepr
+  BASE = { only: [:platform, :code], include: { tag: TagRepr::BASE } }.freeze
+
+  module_function
+
+  def base deerjikist
+    deerjikist.as_json(BASE)
+  end
+
+  def many deerjikists
+    deerjikists.map { |d| base(d) }
+  end
+end
diff --git a/backend/app/representations/WikiPageRepr.rb b/backend/app/representations/wiki_page_repr.rb
similarity index 100%
rename from backend/app/representations/WikiPageRepr.rb
rename to backend/app/representations/wiki_page_repr.rb
diff --git a/backend/config/routes.rb b/backend/config/routes.rb
index 0a52bf9..ed7b4ac 100644
--- a/backend/config/routes.rb
+++ b/backend/config/routes.rb
@@ -9,7 +9,15 @@ Rails.application.routes.draw do
   resources :tags, only: [:index, :show, :update] do
     collection do
       get :autocomplete
-      get 'name/:name', action: :show_by_name
+
+      scope :name do
+        get ':name/deerjikists', action: :deerjikists_by_name
+        get ':name', action: :show_by_name
+      end
+    end
+
+    member do
+      get :deerjikists
     end
   end
 
@@ -54,4 +62,14 @@ Rails.application.routes.draw do
       post 'code/renew', action: :renew
     end
   end
+
+  resources :deerjikists, only: [] do
+    collection do
+      scope ':platform/:code' do
+        get '', action: :show
+        put '', action: :update
+        delete '', action: :destroy
+      end
+    end
+  end
 end
diff --git a/backend/db/migrate/20260303122700_create_deerjikists.rb b/backend/db/migrate/20260303122700_create_deerjikists.rb
new file mode 100644
index 0000000..a87a963
--- /dev/null
+++ b/backend/db/migrate/20260303122700_create_deerjikists.rb
@@ -0,0 +1,10 @@
+class CreateDeerjikists < ActiveRecord::Migration[8.0]
+  def change
+    create_table :deerjikists, primary_key: [:platform, :code] do |t|
+      t.string :platform, null: false, limit: 16
+      t.string :code, null: false
+      t.references :tag, null: false
+      t.timestamps
+    end
+  end
+end
diff --git a/backend/db/schema.rb b/backend/db/schema.rb
index 7a53c81..8077fac 100644
--- a/backend/db/schema.rb
+++ b/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_01_27_005300) do
+ActiveRecord::Schema[8.0].define(version: 2026_03_03_122700) 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
@@ -39,6 +39,15 @@ ActiveRecord::Schema[8.0].define(version: 2026_01_27_005300) do
     t.index ["blob_id", "variation_digest"], name: "index_active_storage_variant_records_uniqueness", unique: true
   end
 
+  create_table "deerjikists", primary_key: ["platform", "code"], charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+    t.string "platform", limit: 16, null: false
+    t.string "code", null: false
+    t.bigint "tag_id", null: false
+    t.datetime "created_at", null: false
+    t.datetime "updated_at", null: false
+    t.index ["tag_id"], name: "index_deerjikists_on_tag_id"
+  end
+
   create_table "ip_addresses", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.binary "ip_address", limit: 16, null: false
     t.boolean "banned", default: false, null: false
diff --git a/backend/lib/tasks/sync_nico.rake b/backend/lib/tasks/sync_nico.rake
index ef37d06..e6b5893 100644
--- a/backend/lib/tasks/sync_nico.rake
+++ b/backend/lib/tasks/sync_nico.rake
@@ -47,7 +47,6 @@ namespace :nico do
     data = JSON.parse(stdout)
     data.each do |datum|
       code = datum['code']
-
       post =
           Post
           .where('url REGEXP ?', "nicovideo\\.jp/watch/#{ Regexp.escape(code) }([^0-9]|$)")
@@ -94,14 +93,15 @@ namespace :nico do
         sync_post_tags!(post, [Tag.tagme.id, Tag.bot.id, Tag.niconico.id, Tag.video.id])
       end
 
-      kept_ids = PostTag.kept.where(post_id: post.id).pluck(:tag_id).to_set
-      kept_non_nico_ids = post.tags.where.not(category: 'nico').pluck(:id).to_set
+      kept_ids = post.tags.pluck(:id).to_set
+      kept_non_nico_ids = post.tags.not_nico.pluck(:id).to_set
 
       desired_nico_ids = []
       desired_non_nico_ids = []
+
       datum['tags'].each do |raw|
         name = "nico:#{ raw }"
-        tag = Tag.find_or_create_by_tag_name!(name, category: 'nico')
+        tag = Tag.find_or_create_by_tag_name!(name, category: :nico)
         desired_nico_ids << tag.id
         unless tag.id.in?(kept_ids)
           linked_ids = tag.linked_tags.pluck(:id)
@@ -109,6 +109,13 @@ namespace :nico do
           desired_nico_ids.concat(linked_ids)
         end
       end
+
+      deerjikist = Deerjikist.find_by(platform: :nico, code: datum['user'])
+      if deerjikist
+        desired_non_nico_ids << deerjikist.tag_id
+        desired_nico_ids << deerjikist.tag_id
+      end
+
       desired_nico_ids.uniq!
 
       desired_all_ids = kept_non_nico_ids.to_a + desired_nico_ids
diff --git a/backend/spec/factories/tags.rb b/backend/spec/factories/tags.rb
index 5d9530e..e2d1120 100644
--- a/backend/spec/factories/tags.rb
+++ b/backend/spec/factories/tags.rb
@@ -1,11 +1,11 @@
 FactoryBot.define do
   factory :tag do
-    category { 'general' }
+    category { :general }
     post_count { 0 }
     association :tag_name
 
     trait :nico do
-      category { 'nico' }
+      category { :nico }
       tag_name { association(:tag_name, name: "nico:#{ SecureRandom.hex(4) }") }
     end
   end
diff --git a/backend/spec/requests/deerjikists_spec.rb b/backend/spec/requests/deerjikists_spec.rb
new file mode 100644
index 0000000..136fc2d
--- /dev/null
+++ b/backend/spec/requests/deerjikists_spec.rb
@@ -0,0 +1,181 @@
+require 'rails_helper'
+
+RSpec.describe 'Deerjikists API', type: :request do
+  let(:platform) { 'nico' }
+  let(:code) { 'deerjika-bot' }
+
+  let!(:tag1) { create(:tag, category: :deerjikist) }
+  let!(:tag2) { create(:tag, category: :deerjikist) }
+
+  let(:member) { create(:user, :member) }
+  let(:guest) { create(:user, role: :guest) }
+
+  describe 'GET /deerjikists/:platform/:code' do
+    subject(:do_request) do
+      get "/deerjikists/#{ platform }/#{ code }"
+    end
+
+    context 'when deerjikist exists' do
+      before do
+        Deerjikist.create!(platform:, code:, tag: tag1)
+      end
+
+      it 'returns 200 and deerjikist json' do
+        do_request
+        expect(response).to have_http_status(:ok)
+
+        expect(json).to be_a(Hash)
+        expect(json['platform']).to eq(platform)
+        expect(json['code']).to eq(code)
+
+        expect(json['tag']).to be_a(Hash)
+        expect(json['tag']['id']).to eq(tag1.id)
+        expect(json['tag']['name']).to eq(tag1.name)
+      end
+    end
+
+    context 'when deerjikist does not exist' do
+      it 'returns 404' do
+        do_request
+        expect(response).to have_http_status(:not_found)
+      end
+    end
+
+    context 'when platform or code become blank after strip' do
+      it 'returns 400' do
+        get '/deerjikists/%20/%20'
+        expect(response).to have_http_status(:bad_request)
+      end
+    end
+  end
+
+  describe 'PUT /deerjikists/:platform/:code' do
+    subject(:do_request) do
+      put "/deerjikists/#{ platform }/#{ code }", params: payload
+    end
+
+    let(:payload) { { tag_id: tag1.id } }
+
+    context 'when not legged in' do
+      it 'returns 401' do
+        sign_out
+        do_request
+        expect(response).to have_http_status(:unauthorized)
+      end
+    end
+
+    context 'when logged in but not member' do
+      it 'returns 403' do
+        sign_in_as guest
+        do_request
+        expect(response).to have_http_status(:forbidden)
+      end
+    end
+
+    context 'when member' do
+      before do
+        sign_in_as member
+      end
+
+      context 'when params invalid' do
+        it 'returns 400 when tag_id is missing or invalid' do
+          put "/deerjikists/#{ platform }/#{ code }", params: { tag_id: 0 }
+          expect(response).to have_http_status(:bad_request)
+        end
+
+        it 'returns 400 when platform or code blank after strip' do
+          put '/deerjikists/%20/%20', params: { tag_id: tag1.id }
+          expect(response).to have_http_status(:bad_request)
+        end
+      end
+
+      context 'when creating new deerjikist' do
+        it 'creates and returns 200 with json' do
+          expect { do_request }.to change { Deerjikist.count }.by(1)
+          expect(response).to have_http_status(:ok)
+
+          d = Deerjikist.find_by(platform:, code:)
+          expect(d).to be_present
+          expect(d.tag_id).to eq(tag1.id)
+
+          expect(json['platform']).to eq(platform)
+          expect(json['code']).to eq(code)
+        end
+      end
+
+      context 'when updating existing deerjikist' do
+        before do
+          Deerjikist.create!(platform:, code:, tag: tag1)
+        end
+
+        let(:payload) { { tag_id: tag2.id } }
+
+        it 'updates tag_id and returns 200' do
+          expect { do_request }.not_to change { Deerjikist.count }
+          expect(response).to have_http_status(:ok)
+
+          d = Deerjikist.find_by(platform:, code:)
+          expect(d.tag_id).to eq(tag2.id)
+
+          expect(json['platform']).to eq(platform)
+          expect(json['code']).to eq(code)
+        end
+      end
+    end
+  end
+
+  describe 'DELETE /deerjikists/:platform/:code' do
+    subject(:do_request) do
+      delete "/deerjikists/#{ platform }/#{ code }"
+    end
+
+    context 'when not logged in' do
+      it 'returns 401' do
+        sign_out
+        do_request
+        expect(response).to have_http_status(:unauthorized)
+      end
+    end
+
+    context 'when logged in but not member' do
+      it 'returns 403' do
+        sign_in_as guest
+        do_request
+        expect(response).to have_http_status(:forbidden)
+      end
+    end
+
+    context 'when member' do
+      before do
+        sign_in_as member
+      end
+
+      it 'returns 400 when platform/code blank after strip' do
+        delete '/deerjikists/%20/%20'
+        expect(response).to have_http_status(:bad_request)
+      end
+
+      context 'when deerjikist exists' do
+        before do
+          Deerjikist.create!(platform: platform, code: code, tag: tag1)
+        end
+
+        it 'destroys and returns 204' do
+          expect {
+            do_request
+          }.to change { Deerjikist.exists?(platform: platform, code: code) }
+            .from(true).to(false)
+
+          expect(response).to have_http_status(:no_content)
+        end
+      end
+
+      context 'when deerjikist does not exist' do
+        it 'returns 404' do
+          do_request
+          expect(response).to have_http_status(:not_found)
+        end
+      end
+    end
+  end
+end
diff --git a/backend/spec/requests/tags_deerjikists_spec.rb b/backend/spec/requests/tags_deerjikists_spec.rb
new file mode 100644
index 0000000..4825f36
--- /dev/null
+++ b/backend/spec/requests/tags_deerjikists_spec.rb
@@ -0,0 +1,102 @@
+require 'rails_helper'
+
+RSpec.describe 'Tags deerjikists API', type: :request do
+  let(:platform1) { 'nico' }
+  let(:code1) { 'deerjika-bot' }
+  let(:platform2) { 'youtube' }
+  let(:code2) { 'deerjika-bot.bsky.social' }
+
+  let!(:tag) { create(:tag, category: :deerjikist) }
+
+  before do
+    # show_by_name / deerjikists_by_name 用に名前を固定
+    tag.tag_name.update!(name: 'deerjika')
+  end
+
+  describe 'GET /tags/:id/deerjikists' do
+    subject(:do_request) do
+      get "/tags/#{ tag_id }/deerjikists"
+    end
+
+    let(:tag_id) { tag.id }
+
+    context 'when tag exists and has no deerjikists' do
+      it 'returns 200 and empty array' do
+        do_request
+        expect(response).to have_http_status(:ok)
+        expect(json).to eq([])
+      end
+    end
+
+    context 'when tag exists and has deerjikists' do
+      before do
+        Deerjikist.create!(platform: platform1, code: code1, tag: tag)
+        Deerjikist.create!(platform: platform2, code: code2, tag: tag)
+      end
+
+      it 'returns 200 and deerjikists array' do
+        do_request
+        expect(response).to have_http_status(:ok)
+
+        expect(json).to be_a(Array)
+        expect(json.size).to eq(2)
+
+        expect(json.map { |h| [h['platform'], h['code']] }).to contain_exactly(
+          [platform1, code1],
+          [platform2, code2],
+        )
+      end
+    end
+
+    context 'when tag does not exist' do
+      let(:tag_id) { 9_999_999 }
+
+      it 'returns 404' do
+        do_request
+        expect(response).to have_http_status(:not_found)
+      end
+    end
+  end
+
+  describe 'GET /tags/name/:name/deerjikists' do
+    subject(:do_request) do
+      get "/tags/name/#{ name }/deerjikists"
+    end
+
+    let(:name) { 'deerjika' }
+
+    context 'when name is blank after strip' do
+      let(:name) { '%20' }
+
+      it 'returns 400' do
+        do_request
+        expect(response).to have_http_status(:bad_request)
+      end
+    end
+
+    context 'when tag does not exist for name' do
+      let(:name) { 'no-such-tag' }
+
+      it 'returns 404' do
+        do_request
+        expect(response).to have_http_status(:not_found)
+      end
+    end
+
+    context 'when tag exists and has deerjikists' do
+      before do
+        Deerjikist.create!(platform: platform1, code: code1, tag: tag)
+      end
+
+      it 'returns 200 and deerjikists array' do
+        do_request
+        expect(response).to have_http_status(:ok)
+
+        expect(json).to be_a(Array)
+        expect(json.size).to eq(1)
+        expect(json[0]['platform']).to eq(platform1)
+        expect(json[0]['code']).to eq(code1)
+      end
+    end
+  end
+end