I'm a girl with a wall up (serial.. hacca)

One day, the protagonist Chaega-eun met her junior Hong Jisoo. She was a very smart class president, and he was a delinquent. As soon as they met, Jisoo fell for Ga-eun and persistently chased after her, leading to a happy ending where they start dating. (Jisoo changes his personality the moment he hears Ga-eun's ideal type is a kind person)