diff --git a/backend/app/models/tag.rb b/backend/app/models/tag.rb
index d496802..26fafec 100644
--- a/backend/app/models/tag.rb
+++ b/backend/app/models/tag.rb
@@ -56,6 +56,12 @@ class Tag < ApplicationRecord
     end
   end
 
+  def self.no_deerjikist
+    @no_deerjikist ||= Tag.find_or_initialize_by(name: 'ニジラー情報不詳') do |tag|
+      tag.category = 'meta'
+    end
+  end
+
   def self.normalise_tags tag_names, with_tagme: true
     tags = tag_names.map do |name|
       pf, cat = CATEGORY_PREFIXES.find { |p, _| name.start_with?(p) } || ['', nil]
@@ -68,6 +74,7 @@ class Tag < ApplicationRecord
       end
     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
   end
 
diff --git a/backend/lib/tasks/sync_nico.rake b/backend/lib/tasks/sync_nico.rake
index d20150c..d604423 100644
--- a/backend/lib/tasks/sync_nico.rake
+++ b/backend/lib/tasks/sync_nico.rake
@@ -1,9 +1,11 @@
 namespace :nico do
   desc 'ニコニコ DB 同期'
   task sync: :environment do
+    require 'json'
+    require 'nokogiri'
     require 'open3'
     require 'open-uri'
-    require 'nokogiri'
+    require 'set'
 
     fetch_thumbnail = -> url do
       html = URI.open(url, read_timeout: 60, 'User-Agent' => 'Mozilla/5.0').read
@@ -87,6 +89,9 @@ namespace :nico do
       if kept_non_nico_ids.to_set != desired_non_nico_ids.to_set
         desired_all_ids << Tag.bot.id
       end
+      unless Tag.where(id: desired_all_ids).where(category: 'deerjikist').exists?
+        desired_all_ids << Tag.no_deerjikist.id
+      end
       desired_all_ids.uniq!
 
       sync_post_tags!(post, desired_all_ids)