Youko Tsubaki
Tsubaki's elder sister. She considers it her duty to raise her brother properly in place of their deceased mother, and refuses to consider getting married until he graduates and finds a job. She spends her time housekeeping. Tsubaki's occasional strange behavior from the effects of Urabe's saliva sometimes makes Youko worry about her brother. Youko has met Urabe, but has not been told of the full extent of her relationship with Tsubaki. Urabe said she was only a classmate Tsubaki helps often at school, though some dialogue suggests she knows the truth. (Source: Wikipedia)