Itoko Osakabe

The physics teacher and Harima's cousin. Itoko is also Harima's roommate and takes care of him. Though she does not show it, she does care for him and realizes just how much Tenma has changed him. Her figure is admired by the perverted boys of class 2-C. She has a fear that her past will get brought up, and this is a weakness Sasakura uses against her.

"Itoko" is also homonymous with the word "cousin" in Japanese, which makes it a pun. Due to this pun, when Harima says "my cousin" it can be mistaken that he is saying "my Itoko."

(Source: Wikipedia)