Last Round Arthurs: Scum Arthur & Heretic Merlin, Vol. 1 (light novel)

Local high school prodigy Rintaro Magami´s daily life is pretty boring, though not for lack of things to do. He´s just...done everything already. In order to kill some time, he deliberately teams up with Luna, the most good-for-nothing girl around, and enters a competition to decide the next successor of the legendary King Arthur. But there´s just one problem... Luna pawned off the holy sword Excalibur!