User blog comment:Iron.Shadow.Dragon/Take Over: Satan Soul origins?/@comment-7418318-20131020104930

It was only stated that Elfman's take-over: beast soul works that way and even that was later revealed to allow a partial take-over by just touching the target.

Lisanna's gravestone read "friend of animal souls" so I highly doubt that her version of take-over would require her to effectively kill and absorb animals, like Elfman's.

With these two being so different, it's likely that take-over: satan soul has yet another mechanic behind it. Because if they work the same way, why would there even be a distinction? There'd be just one all-encompasing take-over magic.

As for possible mechanics for demon take-overs... maybe the caster is going through a ritual that summons a demon to their position and then binds it into their body.