Original (by ZUN):
暗闇の風穴
The Dark Blowhole
Subterranean Animism Stage 1 Theme
Arrangement: Yuma Mizonokuchi (Innocent Key)
Vocals: Ai Ohsera
Circle: セブンスヘブンMAXION (Seventh-Heaven Maxion)
HP:
http://shm.jpn.org/Album: FirstAngriff
Catalogue Number: SHM-0025
Released at 博麗神社例大祭7. (Hakurei Jinja Reitaisai 7)