King's Proposal, Vol. 5 (light novel) — Koushi Tachibana

Surrounded by Man-Eating Monsters…and Women!Mushiki Kuga, having missed the mage aptitude test while out saving the world as Saika, finds himself receiving a failing grade at Void's Garden. His one chance at redemption lies in the hands of Erulka Flaera, who whisks him away to a deserted island crawling with annihilation factors for a one-week supplementary course. However, once he's there, he encounters an altogether different threat…as an adult Erulka and the other members of the course try to seduce him!How will Mushiki escape with both his education and his chastity intact?!