Character Arc
Ranmaru Mori is the centuries-old vampire at the heart of the comedy. Picky to a fault, he only has an appetite for the blood of pure eighteen-year-olds, which is why he has parked himself at the Koi-no-Yu bathhouse with his sights set on a wholesome high-schooler named Rihito. He takes a part-time job there as the perfect cover, biding his time until Rihito's eighteenth birthday so he can finally claim the meal he has been waiting for.
The joke of the series is that Ranmaru is a terrible predator and an enthusiastic babysitter. To keep Rihito pure, he appoints himself the boy's guardian and chaperone, swooping in to derail crushes, sabotage confessions, and panic over every hint of teenage romance. For all his dramatic centuries of experience, he is constantly outmatched by ordinary high-school feelings, and his elaborate schemes tend to backfire into slapstick.
Over the course of the season, Ranmaru's hunger quietly competes with a growing, grudging affection. The longer he watches over Rihito, the more he behaves like a fussy, overprotective family member rather than a monster waiting to strike, and the warmth underneath the gags becomes the real engine of the show.