For this one, in a webcomic I used to read, Homestuck 2, a character named Jade Harley got an outfit that reminded me of something a Touhou character would wear.  So I thought "Maybe I'll draw some pixel art of her in that style."

Upon closer examination of the Touhou sprites, I realized they weren't pixel art at all, just standard sketches shrunk down very small.  So it's more inspired by the way they look than directly in that style.