してんの！ (SHI-TE-N-NO!)

A 4koma series by Fuukadia (narcolepsy). In it, Sakuya Izayoi travels to an alternate dimension version of Gensokyo before the Great Hakurei Barrier was formed to supposedly spy on Yuyuko, but ultimately winds up completely ruining the formation of Gensokyo with the help of the bumbling big four oni. (Ibuki Suika, Hoshiguma Yuugi, Ibaraki Kasen, and, as a "replacement oni", Konngara)

Hilarity Ensues.

See also its pixpedia and Nicopedia article.