Chitose Mikado

Chitose Mikado (御門 千歳 Mikado Chitose) is the twin sister of Chihaya Kisakinomiya who died of a disease that identical twins are susceptible to at ten years old.

Taeko Mikado
Taeko is Chitose's mother who she possibly called her "mama".

Chihaya Kisakinomiya
Chihaya is Chitose's twin brother who called "Chi-chan" where she took care of Chihaya during her lifetime, but she appears as a ghost and she supports him.