Kaya

A zashiki-warashi (a child's spirit that resides in a tatami mat) who serves the Amakawa family. She lives in Yuuto's grandparents house. She is extremely fond of Himari and often threatens Yuuto whenever he gets close to Himari and she said darkly that she would rather have him dead because Himari had to leave because of him. She's the one that supplied Shizuku with Amakawa's family book, which contains information about the family itself and Himari.