owl＊tree has acknowledged the video at least through the following tweets: "Wow" (https://twitter.com/owltree_pvq/status/1386188649650294784) & "WTF!! 700,000 views Over!?" (https://twitter.com/owltree_pvq/status/1422191103957082118)
The arranger of Shuric Scan has acknowledged this video at least through the following YouTube comment (https://www.youtube.com/watch?v=3x8jlCz0jw0&lc=UgwtukkkqzM7xZDrPEd4AaABAg.9b8PeGipCsx9gYoSWC8IQd): "Truth: 1. I made a cover of Ninja Gaiden II OST for TSRh team. 2. tPORt team used it in Shuric Scan keygen. 3. tomgoodmen created his video "manwith10scans" based on my cover."
I assume the Niconico URL (https://web.archive.org/web/20210228124052/https://www.nicovideo.jp/watch/sm15516751) to be correct based on the matching title (See here: https://twitter.com/hashtag/sm15516751) and length as well as tags mentioning Zen, stein and Animal Crossing.
Twitter results related to the original Niconico upload (https://twitter.com/hashtag/sm15988513) imply that the video was originally titled "AND" before being renamed to "FUN藤さん" later on.
10. [YTPMV] Holy Perplexity, Batman!: A couple of old tweets (https://twitter.com/ouh80hwr/status/20458198273 & https://twitter.com/rcatstott/status/340705963730432000) link to a YouTube video by this name (https://www.youtube.com/watch?v=BWudvvfLuyI), but no archives seem to exist to provide information regarding its creator or upload date. The earliest tweet implies that it was around by 2010/08/06.
An archived page of Mestre3224's channel from 2011/07/05 (https://web.archive.org/web/20110705100808/http://www.youtube.com/user/Mestre3224) shows that the video's original title was "YTPMVBR - 1300 Subs" and its original ID was "3LlXiPWwfaY". Its original video page has not been archived. It was originally uploaded sometime between 2011/05/11-05/17, based on the video uploaded just prior to it (https://web.archive.org/web/20111027045559/http://www.youtube.com/watch?v=RqA8maJ2Jxo) and a tweet linking it (https://twitter.com/sweetdreams1993/status/70385845173104640).
While I can confirm that user/118374604 was named 手ブラ at one point, the name's general-ness leaves it uncertain whether or not user/132656764 is the exact same user. There's a choice to split the two channels in two tags if it remains uncertain enough.