Extra Stage boss. Like her elder sister Satori, she was born with the power to read other people's minds. However, Koishi knew this power of hers would make people feel uneasy around her, so she deliberately closed off this power. She sealed away her own heart to others in doing so, and even her sister would not be able to read her heart. Satori took pity on her, and gave some pets to Koishi, hoping that the animals would open Koishi's heart to others.