18+ Kinsou no Vermeil: Gakeppuchi Majutsushi wa Saikyou no Yakusai to Mahou Sekai wo Tsukisusumu

Alto, an aspiring magician, is about to repeat a grade when he accidentally summons the demon Vermeil, which was sealed in a book Alto found by chance. Not only does Vermeil hold an ancient power capable of bringing about the end of the world, she's also quite naughty! A traditional fantasy story about a struggling magician and his powerful familiar begins with their fateful meeting!

(Source: Square Enix)