King's Proposal, Vol. 5 (novel)

When Mushiki Kuga misses Void Garden’s magicians’ aptitude exam while subduing annihilation factors as Saika, he receives a notice that he will be held back. To make sure he can move on to the next year, he is made to take a week of supplementary lessons at Nirai Island under Erulka’s guidance. But there, Mushiki soon discovers that he will have more than just his grades to worry about...because everyone else who’s come to the island is trying to seduce him! It’s time to avoid expulsion and protect his chastity!