Mina Sato

She thought Ai was after Yuichiro, the guy she liked, so she turned the whole girl population against Ai. But later on after she finds out Ai likes Ichinose and not Kato they become best friends. The reason why Yuichiro dislikes her is actually because of an incident that happened when they were left in a classroom together in junior high. Yuichiro had tried to shy away from her though she never stops chasing after him. She's aware of his feelings for Ai. She hates the fact that he does but there's one event in the manga where she tells him to just to tell Ai that he loves her. Mina's usually vulgar like Sou and like Ai said she has a tiger like personality and was ready to pounce any time. Her feelings for Yuichiro are very obvious and she knows so much about him, it almost looks like she's stalking him. (Source: Wikipedia)