Thread:Hitsuji Mamoru/@comment-30314236-20180822154337/@comment-34364075-20181006134739

I'm pretty sure it's mentioned in Heaven's Feel (in the VN at least. Haven't watched the movie yet).

Basically Zouken can transfer his soul to a parasite bug, which may then be used to take over people's bodies. Essentially he's capable of swapping bodies I suppose.