Japanese Title: 東方陰陽鉄
Alternate Title: 陰陽鉄を勝手にコミカライズ ("I turned Iron of Yin and Yang into a comic because I felt like it")
Artist: Mr. Pavlov
Artist's pixiv: Here
A certain elf from Final Fantasy XI crash lands into Reimu's donation box. Marisa steals his precious thing. Stuff happens.
Based on this particular set of NicoNico videos: Link
pool #3290 -Meiling and Naitou side story (Artist-created)