@GoodWorld Is our masked misanthrope really even a kidnapper? I mean, yes, he calls himself that, but let us look at the actual facts.
He asked her to come with him. No force or threats were used to attain her cooperation.
He leaves her unattended with the door unlocked. No effort is made at imprisonment. If she ever wants to leave, she just has to walk out the door. while he's asleep or at work
This is enhanced by the fact that her parents(such as they are) have kept the area agitated, so people are looking for her. If she leaves, it will be trivial to ensure she never meets him again.
Basically, she went with him because she wanted to, and she stays with him because she still wants to. Is that what you call kidnapping?
From a technical, legal standpoint, I'd say he is guilty of harboring a runaway, not kidnapping. Where I'm from, that is a crime, but it is a different and less serious one. (I acknowledge japanese law may consider the two equivalent.) He's unarguably a stalker. But again, that's a different crime.
From a moral standpoint... he's a hero risking his life to protect her from a society that is conspiring with a pair of horrifying monsters, of the kind you occasionally see in the news after it is too late. Granted, he didn't set out to be a hero, but results matter.
If he were actually presented as a kidnapper, I would've dropped this like a hot potato. A disgustingly moldy hot potato.