So Ren is some kind of
summon Hero (or maybe a True Hero)
, that's why Mary is afraid of him using anything sharp, since she thinks he will
demolish everything with his power
, as seen when he first grabbed the kitchen knife.
This would explain why Neah opposed Ren living with Mary, since Ren is probably
; if this is the case we won't see anything chapter from Mary's perspective, since that would spoil the
.