Okusama ga Seito Kaichou!

Hayato Izumi is running for student council president. He's studious, responsible, down to earth...and completely outmatched by his rival, Ui Wakana. Ui wins in a landslide after promising comprehensive sex education, free condoms, and other exciting reforms. Bloodied but not discouraged, Hayato licks his wounds and settles for vice president. Then Ui moves in with him. As it turns out, their parents made a drunken promise decades ago that their children would one day marry. Ui and Hayato must now balance school life with matrimony, keeping their relationship secret from a prudish student body and learning to live with each other. Can they keep the student council in line and find happiness together? Find out in Okusama ga Seitokaichou!(Source: MyAnimeList)