I think the heart belongs to someone we haven’t meet yet and this could be how MM fingerprints got in the box. EQ could have showed her the box with heart in FTL and this could be why SW is trying so hard to kill her in the next episode. There is a lot more going on between those two then EQ killing SW father and trying to kill her and whatever SW did to the EQ, that might have started but the EQ has escalated it into a very no rules war. Maybe the design of the box are copies of some box SW’s mother had and the heart in the box is SW’s mother. Just throwing ideas out there; which are probable wrong, but I really want to know why they hate each other so deeply.