Make the heroine act psypathic (Is this even a word) and less horny is a good idea.
Dude is like 5 years old, even after reincarnated, I doubt he can feel anything but fear from a Yandere.
the only solution for a yandere is to break her... break her with that massive dragon. make her a slave to it, so that all she can think of is getting railed.no time to get murderous obsessive thoughts then xd