The demonic god-queen of Makai and the last boss of the fifth Touhou PC-98 game, Mystic Square. She created Makai and everything in it. She is thus considered to be the mother or foster-mother of Alice Margatroid, the stage 3 boss of Mystic Square and also the Extra stage boss.
She is sometimes depicted as being friends with Undefined Fantastic Object's last boss, Hijiri Byakuren, since one of her attacks, "Devil's Recitation", is a spellcard version of Shinki's final bullet pattern from Mystic Square. Since Byakuren was sealed in a portion of Makai, this effectively made Shinki her jailer, granting them an opportunity to interact.
