Sakuya's character design seems heavily based off of the Seihou character Muse (who just happens to be my avatar because she's awesome). She came from Kioh Gyoku, which was released in 2001, one year before EoSD. She has short grey hair and a blue/white frilly dress. She also happens to use knife throwing and manipulation of cursed marionettes(Alice?) as the base for her danmaku. So that makes Yumeko, Dio Brando, and Muse. I guess Sakuya is just a big old bag of homages isn't she?