Watashi yori Tsuyoi Otoko to Kekkon Shitai no

Akira Kogure, a boy who was a bit of a nerd, accidentally discovered that the beautiful student council president, Shizuka Takasaki, used to be a delinquent girl-gang leader. She said she would only marry a man who was stronger than her. But it turned out that Akira was actually also a former delinquent even stronger than her. (Source: Fantasia Bunko, translated)