Hahahaha, the doll really is cursed and can steal the soul of a person... but Lily has two souls in her, and that soul is strong enough to overpower the doll, that is a funny loophole.
Hajime not giving a rat's ass to the situation cracks me up, he is confident he can smash his way trough anything that comes... but the house turning into a dungeon is unexpected, maybe the person that made the doll is some sort of mage, a quite powerful one it seems.