“Deleted Video” (削除動画, Sakujo Douga) was the short clip that Niconico would play in place of videos that were deleted or taken down, while still letting users comment and view the video's statistics. The feature would be formally retired around March 2020 after a website overhaul.¹⁾²⁾

The video would feature white text scrolling on a black background, read by a female narrator, with a rendition of either Hotaru no Hikari (蛍の光) or Sakura no Ume (桜ノ雨) by “Foo-san” (Fooさん). The thumbnail initially read “maybe it's been deleted?” (削除されたかも？), then it became “can't watch” (視聴できません) for several years, then it was last changed to a generic thumbnail in 2018 before it was discontinued.

Copyright claim.

Deleted by uploader.

Over the years, Niconico Douga users would make MAD videos, parodies, and remixes of these videos. One notable example was ".",³⁾⁴⁾ or “it's all your fault.” (全てあなたの所為です。, subete anata no sei desu.), which briefly inspired the "SubeAna-style" (すべあな風) trend. Aside from that, there's mostly just sentence mixing, and recorder/harmonica renditions deserving of a “Foo-san” (Fooさん) tag.

• If you're new to Japanese, the kanji being bigger than the hiragana and katakana is quite normal.
• Hotaru no Hikari borrows the melody of the Scottish song, Auld Lang Syne, so you may have some English speakers that end up hearing the “should old acquaintance be forgot” lyric instead.
• Unfortunately, the video's discontinuation meant that it was now difficult to track which videos had over 100,000 or 1,000,000 views, unless you look for the video's metadata on websites like Nicolog.

• Official Deleted Video on Niconico Encyclopedia
• @foo_san on Twitter