Kotomi Komiyama is Tomoko and Yuu's classmate in middle school. She and Tomoko do not like each other very much and are usually forced to get along with each other when Yuu is around. She attends the same high school, Makuhari Shuuei High School, as Tomoko, though Tomoko had more or less completely forgotten about her. She has a crush on Tomoki, but Tomoko seemingly more or less ruined her chances of being with him.
Kotomi is a shy girl but does not have the difficulty with social interactions that Tomoko has. If given the chance, she will willingly pontificate upon baseball and her favorite team to anyone. Much of her character is depicted reacting to Tomoko, making her appear resentful, judgmental, and jealous. However, she appears a much nicer person to other people. Despite her sometimes petty-level rivalry with Tomoko, she does not truly hate her. She can also become friends with her potential rival for Tomoki.
(Source: WataMote Wikia)