i think either he captured her soul (probably after killing her) or he kidnapped her & faked her death. he's up to something big. maybe he's one of the gods of death or someone trying to become one? or maybe he's another part of mc's soul (so there are 8 missing parts)? maybe grandma summoned him? they haven't explained how she got the energy jawbreakers yet.
Oh I'm loving these theories so far. I would assume the grandma knew how to defeat those beings and turn them into those jawbreakers as you called them for MC when he was little. But also the fact that some time should have passed, a few years i think since her death yet her body still looks the same as when he was a child is so odd.
The ending for this chapter, those statues would definitely scare me lol. Also was that his grandmother, the one that's apparently dead that the black haired dude took out of what looked like a closet?? Clearly his ass is sus but wtf