Last Round Arthurs, Vol. 1 (manga) — Taro Hitsuji

For as long as he can remember, Rintarou Magami has been able to do everything perfectly -- but life as a genius is boring. That's why when he hears about a battle to determine King Arthur's successor, he decides to have a little fun and join forces with the weakest candidate, Luna Artur. The only problem: Luna already sold her Excalibur for cash! As the nighttime battles of swords and sorcery intensify, will Rintarou regret backing such an utter scumbag?