These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
YMMV: Yuugen Kaisha
Fridge Horror: Not only will Bosco likely outlive Makiko by centuries, she also needs to stay a virgin for him to feed on her blood.
Fridge Brilliance: On the other hand, limiting himself to feeding only 4 times a year could potentially shorten Bosco's lifespan, given it's already made him anemic and has left him without much of the vampiric enhanced strength he'd have if he fed normally.
Alternatively, assuming Makiko's willing, he could always turn her. But it doesn't seem like the sort of thing he'd do, since he was trying to become human (or as close to it as he could get) for her sake.