Watashi yori Tsuyoi Otoko to Kekkonshitai no: Seiso na Bijin Seitokaichou (Jitsu wa Moto Banchou) no Himitsu wo Shiru Inkya (Jitsu wa Kanojo wo Koeru Saikyou no Yankee) (Light Novel)

As a result of an unexpected event, Akira Kogure - an introverted and lonely young man - discovers that the beautiful student council president, Shizuku Takasaki, is secretly the former female head of a gang. She apparently wants to marry a man who's stronger than her, but what she doesn't know is that Akira was a juvenile delinquent whose strength surpassed even hers...