I do not get it.
This guy has discovered how to be immortal by reincarnating in other people's bodies.
Why he nor anyone near him and even other people just knowing it do not suggest him to reincarnate into his own toddlers?
It would be totally legit in a world in which children are already been forced to work, kill and do war.
It would not be that bad: reproduction would be then considered as cloning and it would become normal in a few generations.
If even in real life we legitimately "kill" fetuses to get stem cells, why would then be a problem to clone people into newborns?
With widespread immortality ninja wars would make no sense and everyone would live peacefully.