Class no Daikirai na Joshi to Kekkon Suru Koto ni Natta.

The light novel that inspired a manga—also from Seven Seas—and an anime! What happens when you get hitched to your nemesis? One newlywed student couple must figure out how to live in harmony in this hilarious rom-com!
Archenemies Hojou Saito and Sakuramori Akane have a notorious reputation as bitter rivals at their high school. Without fail, the two can be found bickering and arguing every day, making school their own personal battleground. But their relationship takes a drastic turn when Saito’s domineering grandfather delivers a shocking ultimatum: marry his rival or lose the family business to the dog! Saito reluctantly accepts his fate, and to his complete surprise, Akane agrees without a fight. And just like that, they’re a married couple! Now, these rivals-turned-newlyweds must navigate living under the same roof and sharing meals (and a bed!) all without tearing each other apart. Can they manage to live together in peace and keep their embarrassing circumstances a secret from their classmates?

[From Seven Seas Entertainment]