Original (by ZUN):
亡き王女の為のセプテット
Septette for the Dead Princess
Remilia Scarlet's Theme
Embodiment of Scarlet Devil Stage 6
Vocals: Shizuku Aosaki
Circle: Iemitsu.
HP:
http://iemitsu.net/Album: Re7-G-
Catalogue Number: SICD-052
Released at Comiket 77.