Tomo, a young kindergartner, is the illegitimate child of Tomoyo's father and another woman named Yūko Mishima. It is eventually decided that Tomo will live in Tomoyo's apartment for the time being. Tomoyo loves her very much and takes care of her constantly since she always had a weakness for children. The reason Tomo came to live with Tomoyo is due to her mother suffering from psychological problems which result in a weak mind. Her mother's state agonized Tomo to the point where she had to move in with Tomoyo.