diff --git a/backend/app/models/tag.rb b/backend/app/models/tag.rb
index 14555a7..83afbd3 100644
--- a/backend/app/models/tag.rb
+++ b/backend/app/models/tag.rb
@@ -76,6 +76,10 @@ class Tag < ApplicationRecord
     @bot ||= find_or_create_by_tag_name!('bot操作', category: :meta)
   end
 
+  def self.no_deerjikist
+    @no_deerjikist ||= find_or_create_by_tag_name!('ニジラー情報不詳', category: :meta)
+  end
+
   def self.video
     @video ||= find_or_create_by_tag_name!('動画', category: :meta)
   end
@@ -100,6 +104,7 @@ class Tag < ApplicationRecord
     end
 
     tags << Tag.tagme if with_tagme && tags.size < 10 && tags.none?(Tag.tagme)
+    tags << Tag.no_deerjikist if tags.all? { |t| t.category != 'deerjikist' }
     tags.uniq(&:id)
   end
 
diff --git a/backend/lib/tasks/sync_nico.rake b/backend/lib/tasks/sync_nico.rake
index b726ac1..6ee9c26 100644
--- a/backend/lib/tasks/sync_nico.rake
+++ b/backend/lib/tasks/sync_nico.rake
@@ -2,9 +2,9 @@ namespace :nico do
   desc 'ニコニコ DB 同期'
   task sync: :environment do
     require 'json'
-    require 'open3'
-    require 'open-uri'
     require 'nokogiri'
+    require 'open-uri'
+    require 'open3'
     require 'set'
     require 'time'
 
@@ -15,12 +15,12 @@ namespace :nico do
       doc.at('meta[name="thumbnail"]')&.[]('content').presence
     end
 
-    def sync_post_tags! post, desired_tag_ids, current_ids: nil
-      current_ids ||= PostTag.kept.where(post_id: post.id).pluck(:tag_id).to_set
-      desired_ids = desired_tag_ids.compact.to_set
+    def sync_post_tags! post, desired_tag_ids, current_tag_ids: nil
+      current_tag_ids ||= PostTag.kept.where(post_id: post.id).pluck(:tag_id).to_set
+      desired_tag_ids = desired_tag_ids.compact.to_set
 
-      to_add = desired_ids - current_ids
-      to_remove = current_ids - desired_ids
+      to_add = desired_tag_ids - current_tag_ids
+      to_remove = current_tag_ids - desired_tag_ids
 
       Tag.where(id: to_add.to_a).find_each do |tag|
         begin
@@ -42,7 +42,10 @@ namespace :nico do
         { 'MYSQL_USER' => mysql_user, 'MYSQL_PASS' => mysql_pass },
         'python3', "#{ nizika_nico_path }/get_videos.py")
 
-    abort unless status.success?
+    unless status.success?
+      warn stderr
+      abort
+    end
 
     data = JSON.parse(stdout)
     data.each do |datum|
@@ -93,40 +96,50 @@ namespace :nico do
         sync_post_tags!(post, [Tag.tagme.id, Tag.bot.id, Tag.niconico.id, Tag.video.id])
       end
 
-      kept_ids = post.tags.pluck(:id).to_set
-      kept_non_nico_ids = post.tags.not_nico.pluck(:id).to_set
+      tags = post.tags
+      # 既存のタグ Id. 集合
+      kept_tag_ids = tags.pluck(:id).to_set
+      # うち内部タグ Id. 集合
+      kept_non_nico_tag_ids = tags.not_nico.pluck(:id).to_set
 
-      desired_nico_ids = []
-      desired_non_nico_ids = []
+      # 記載すべき外部タグ Id. および連携される内部タグ Id. のリスト
+      desired_nico_tag_based_ids = []
+      # 記載すべき内部タグ Id. のリスト
+      desired_non_nico_tag_ids = []
 
       datum['tags'].each do |raw|
         name = "nico:#{ raw }"
         tag = Tag.find_or_create_by_tag_name!(name, category: :nico)
-        desired_nico_ids << tag.id
-        unless tag.id.in?(kept_ids)
+        desired_nico_tag_based_ids << tag.id
+
+        # 新たに記載される外部タグと連携される内部タグを記載
+        unless tag.id.in?(kept_tag_ids)
           linked_ids = tag.linked_tags.pluck(:id)
-          desired_non_nico_ids.concat(linked_ids)
-          desired_nico_ids.concat(linked_ids)
+          desired_non_nico_tag_ids.concat(linked_ids)
+          desired_nico_tag_based_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
+        desired_non_nico_tag_ids << deerjikist.tag_id
+        desired_nico_tag_based_ids << deerjikist.tag_id
+      elsif !(Tag.where(id: kept_non_nico_tag_ids).where(category: :deerjikist).exists?)
+        desired_non_nico_tag_ids << Tag.no_deerjikist.id
+        desired_nico_tag_based_ids << Tag.no_deerjikist.id
       end
 
-      desired_nico_ids.uniq!
+      desired_nico_tag_based_ids.uniq!
 
-      desired_all_ids = kept_non_nico_ids.to_a + desired_nico_ids
-      desired_non_nico_ids.concat(kept_non_nico_ids.to_a)
-      desired_non_nico_ids.uniq!
-      if kept_non_nico_ids.to_set != desired_non_nico_ids.to_set
-        desired_all_ids << Tag.bot.id
+      desired_all_tag_ids = kept_non_nico_tag_ids.to_a + desired_nico_tag_based_ids
+      desired_non_nico_tag_ids.concat(kept_non_nico_tag_ids.to_a)
+      desired_non_nico_tag_ids.uniq!
+      if kept_non_nico_tag_ids != desired_non_nico_tag_ids.to_set
+        desired_all_tag_ids << Tag.bot.id
       end
-      desired_all_ids.uniq!
+      desired_all_tag_ids.uniq!
 
-      sync_post_tags!(post, desired_all_ids, current_ids: kept_ids)
+      sync_post_tags!(post, desired_all_tag_ids, current_tag_ids: kept_tag_ids)
     end
   end
 end