This is really cute! I'm sure things will get rolling once we're properly introduced to the rest of the main cast, but I kind of hope this continues on for a while longer as an absurd slice of life.
My guess is moreso they knew her weakness was fire (since that's what they traumatized/tortured her with) and just picked a decent, mid-ranked fire-based Hunter that could be easily persuaded - at least, easier to persuade/control than an A rank or better would be, I suppose
This is really nice, I like the vibes and hope they’ll last for as long as possible! Before the story decides to gear up and get serious later down the line lol. Also, how does the chef stay in the demon world? Does MC purify him consistently?