diff --git a/backend/app/models/tag.rb b/backend/app/models/tag.rb
index e772e9c..c4b36e6 100644
--- a/backend/app/models/tag.rb
+++ b/backend/app/models/tag.rb
@@ -67,9 +67,17 @@ class Tag < ApplicationRecord
     @bot ||= find_or_create_by_tag_name!('bot操作', category: :meta)
   end
 
+  def self.video
+    @video ||= find_or_create_by_tag_name!('動画', category: :meta)
+  end
+
+  def self.niconico
+    @niconico ||= find_or_create_by_tag_name!('ニコニコ', category: :meta)
+  end
+
   def self.normalise_tags tag_names, with_tagme: true, deny_nico: true
     if deny_nico && tag_names.any? { |n| n.start_with?('nico:') }
-      raise NicoTagNormalisationError 
+      raise NicoTagNormalisationError
     end
 
     tags = tag_names.map do |name|
diff --git a/backend/lib/tasks/sync_nico.rake b/backend/lib/tasks/sync_nico.rake
index 86bd941..b3596cb 100644
--- a/backend/lib/tasks/sync_nico.rake
+++ b/backend/lib/tasks/sync_nico.rake
@@ -1,10 +1,12 @@
 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 'set'
+    require 'time'
 
     fetch_thumbnail = -> url do
       html = URI.open(url, read_timeout: 60, 'User-Agent' => 'Mozilla/5.0').read
@@ -45,13 +47,42 @@ 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]|$)")
-                 .first
-      unless post
-        title = datum['title']
+
+      post =
+          Post
+          .where('url REGEXP ?', "nicovideo\\.jp/watch/#{ Regexp.escape(code) }([^0-9]|$)")
+          .first
+
+      title = datum['title']
+      original_created_at = datum['uploaded_at'] &&
+          Time.strptime(datum['uploaded_at'], '%Y-%m-%d %H:%M:%S')
+      original_created_from = original_created_at&.change(sec: 0)
+      original_created_before = original_created_from&.+(1.minute)
+
+      if post
+        attrs = { title:, original_created_from:, original_created_before: }
+
+        unless post.thumbnail.attached?
+          thumbnail_base = fetch_thumbnail.(post.url) rescue nil
+          if thumbnail_base.present?
+            post.thumbnail.attach(
+                io:           URI.open(thumbnail_base),
+                filename:     File.basename(URI.parse(thumbnail_base).path),
+                content_type: 'image/jpeg')
+            attrs[:thumbnail_base] = thumbnail_base
+          end
+        end
+
+        post.assign_attributes(attrs)
+        if post.changed?
+          post.save!
+          post.resized_thumbnail! if post.thumbnail.attached?
+        end
+      else
         url = "https://www.nicovideo.jp/watch/#{ code }"
         thumbnail_base = fetch_thumbnail.(url) rescue nil
-        post = Post.new(title:, url:, thumbnail_base:, uploaded_user: nil)
+        post = Post.new(title:, url:, thumbnail_base:, uploaded_user: nil,
+                        original_created_from:, original_created_before:)
         if thumbnail_base.present?
           post.thumbnail.attach(
               io:           URI.open(thumbnail_base),
@@ -60,7 +91,7 @@ namespace :nico do
         end
         post.save!
         post.resized_thumbnail!
-        sync_post_tags!(post, [Tag.tagme.id])
+        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
diff --git a/backend/spec/tasks/nico_sync_spec.rb b/backend/spec/tasks/nico_sync_spec.rb
index e4cef17..daa243e 100644
--- a/backend/spec/tasks/nico_sync_spec.rb
+++ b/backend/spec/tasks/nico_sync_spec.rb
@@ -13,7 +13,6 @@ RSpec.describe "nico:sync" do
   end
 
   def link_nico_to_tag!(nico_tag, tag)
-    # NicoTagRelation がある前提（君の model からそう見える）
     NicoTagRelation.create!(nico_tag_id: nico_tag.id, tag_id: tag.id)
   end
 
@@ -35,7 +34,12 @@ RSpec.describe "nico:sync" do
     Tag.tagme
 
     # pythonの出力（AAA が付く）
-    stub_python([{ "code" => "sm9", "title" => "t", "tags" => ["AAA"] }])
+    stub_python([{
+        'code' => 'sm9',
+        'title' => 't',
+        'tags' => ['AAA'],
+        'uploaded_at' => '2026-01-01 12:34:56',
+        'deleted_at' => '2026-01-31 00:00:00' }])
 
     # 外部HTTPは今回「既存 post なので呼ばれない」はずだが、念のため塞ぐ
     allow(URI).to receive(:open).and_return(StringIO.new("<html></html>"))
@@ -49,6 +53,9 @@ RSpec.describe "nico:sync" do
     expect(active_tag_names).to include("nico:AAA")
     expect(active_tag_names).to include("spec_linked")
 
+    expect(post.original_created_from).to eq(Time.iso8601('2026-01-01T03:34:00Z'))
+    expect(post.original_created_before).to eq(Time.iso8601('2026-01-01T03:35:00Z'))
+
     # 差分が出るので bot が付く（kept_non_nico_ids != desired_non_nico_ids）
     expect(active_tag_names).to include("bot操作")
   end