There's the unidentified blonde girl again...

Maybe artist self-insert ?

It might be Satsuki Rin

Looks a bit like Satsuki Rin.

Satsuki_Rin is plausible, but she has neither long hair nor twintails.

The Blond girl is Nix from the fan game "東方幕華祭　～ Fantastic Danmaku Festival", a remastering of EotSD. She replaces Rumia as the stage one boss and Sakuya as the stage 6 mid boss. No translation for the game is up so i don't know much about her.

I see. Thanks.