Touhou Project Side Story (Hoshi no Kioku, literally “Memory of Stars”) is a 50-minute fan-made animated video created by SOUND HOLIC and released at Comiket 73 in December 2007. Its plot involves Kaguya Houraisan, Eirin Yagokoro, Reisen Udongein Inaba and Sakuya Izayoi traveling back to the Moon to confront Kaguya’s father, Luna Marius. The character animation is fairly rudimentary, but it makes extensive use of analog video effects.
The video was in production before Lunarian civilization was first canonically shown in Silent Sinner in Blue, which contradicts it. This movie’s portrayal of the Lunarians, the Earth-Moon war, the Hourai Elixir and Kaguya and Eirin’s parents should be considered non-canon.