Last Round Arthurs (2018)

Blurb:
“I sold my Excalibur … for money.”

In all honesty, Rintarou’s life is boring as hell. If you ask him, he was born into this world with too much talent. Everything goes according to his plan. His way of having fun? Joining forces with the weakest candidate, Luna Artur, in the upcoming battle to become King Arthur’s successor—and save the world from impending doom.

The only problem? She’s the scummiest of scum, pawning off her sacred sword and forcing her knight, Sir Kay, into some seriously skeevy cosplays! Or so he thinks until a close encounter with death, when her true power astonishes all. Make way for an unexpected take on the age-old legends of King Arthur!

Source: www.anisearch.com/manga/43923