The Ayatsuri Incident ~Mystery Shadow~ (アヤツリ異変(いへん) ～ナゾの影(かげ)～)¹⁾ was a fan-made Touhou Project series, authored by “Rīna” (りーな) in Flipnote Studio 3D from 2014 to 2015. The series has the short name of Memo☆ (メッモー☆, Memmō☆), the game's Japanese name.

A mysterious character named Miramikaru Riran, the Mischievous Fox of Terror, enters Gensōkyō and causes trouble by inflicting Cirno with 'insanity'. She makes Cirno fight Daiyousei at the Hakurei Shrine, then rumors began spreading. Riran proceeds to Koumakan, uses her 'Dark Inferno' spell card against Koakuma, which led to Remilia insisting that Flandre should take shelter in the basement, which she reluctantly complies.

Shortly after, Sakuya returns from a shopping trip to get a briefing of their ongoing situation, then Marisa stops by the basement and invites Flandre to solve the incident with her tomorrow morning. The series ends on a cliffhanger where Cirno explains to Riran that they only became 'friends' as a consequence of her losing, which frustrates Riran who vows to inflict 'despair' and 'fear'.

Memo☆ was a project amongst a group of elementary and middle school students that, despite what one may expect, came off as a fairly well-executed series. The series was first re-uploaded to Niconico Douga without permission on July 6, 2015, with said uploader adding Honobono Jinja and locking-in the 'Cookie☆' tag to force the association,²⁾ but it underperformed since Kusso☆ S3 was getting big at the time.

At some point, Rina had a Twitter account and did chat with the Cookie☆ community, but had to stop since her parents were concerned due to her young age. The series continued, with a stipulation that further re-uploads to Niconico were no longer allowed or else she would cancel the series. Of course, the internet did just that, so the series abruptly ended on a cliffhanger after Episode 11.

The Past Arc Manga (過去編(かこへん)漫画)³⁾ is a prequel to the Ayatsuri Incident with no voice acting. It follows Riran and Miran, two sisters with the ability to invoke 'insanity', but the story abruptly ends after Miran's first day in Class 1-D of 'Misfortune High School' (薄命高校). Given the warnings, the prequel was planned to have some kind of 'depressing' turn, but it was never completed so we're simply left to speculate.

• For the record, Rina was reportedly born on February 26, 2004, so she would have been 11 years old when the first few episodes were re-uploaded to Niconico without her permission.
• In Episode 9 and 10, 'Egg Sushi' (玉子寿司くん, Tamago Sushi-kun) has a few subliminal appearances when a brown-haired Fairy Maid and Marisa individually speak with Flandre.
• Over the years, there have been a number of jokes about Riran inspiring other characters:
  • With the release of Touhou Kanjuden in 2015, it was joked that Riran served as the inspiration for Clownpiece (e.g. 'insanity' ability, 'inferno' spell card) and Junko (e.g. blonde fox).
  • When the Senko-san manga initially published in 2017, it was joked that the titular character was Riran, which gained even more traction after it received an anime adaptation in 2019.
• Miran is meant to be Riran's blue-haired little sister, identifiable by her numerous hair accessories.

• KusoKuri☆ - This voice drama has a Riran cameo which has contributed to her popularity.

• Ayatsuri Incident #1-9 → #10 → #11 - The original (once unauthorized) re-uploads.
  • Ayatsuri Incident ☆Complete Version☆ - The unsplit, unmodified compilation.
  • Ayatsuri Incident #1-10 → #11 (English Subs)
• Ayatsuri Prequel Manga #1 → #2 - The one with Riran's younger sister, Miramikaru Miran.
  • Ayatsuri Prequel Manga #1 → #2 (English Subs)
• Memo☆ on the Cookie☆ Explanation Wiki
• Memo☆ Transcript on the Cookie☆ Jikkyou Wiki - This goes up to Episode 9.