御門 千歳

Chitose is Chihaya's twin sister. She died of a disease that identical twins are susceptible to at ten years old. She took care of Chihaya during her lifetime. 
She will appear as a ghost and support him also during the game. /

Taken from url=http://en.wikipedia.org/wiki/List_of_Otome_wa_Boku_ni_Koishiteru_characters#Otome_wa_Boku_ni_Koishiteru:_Futari_no_Elder.