That was dumb af. Seriously? His wife KNOWS that he's strong enough to defeat her and get the demon king to personally come and recruit him, but he needs to be protected from a random demon? Come on now.
"iT iS dAnGeRoUs tO tElL aN iNdIvIdUaL oF tHe DeMoN rAcE aBoUt YoUr pUrIfIcAtIoN mAgIc"
He is literally infinitely powerful, what danger would anything pose to him? This plot is so fucking forced.