The art style of the long-haired Kogasa reminds me of Koishi Komeiji's Heart-Throbbing Adventure, though I can't confirm it's meant to be fanwork of the series.

It's not meant to be fanart of KHTA. It's a second...Kogasa, I think you'd say. Tatari Kogasa, lit. Cursed Kogasa

bifrst likes dark Touhous, and they've worked on a few KKHTA fanart before, so that's why.

Black_Gold_Saw said:
bifrst likes dark Touhous, and they've worked on a few KKHTA fanart before, so that's why.

That makes sense, thank you very much.