Well, in the first round, the child decided to commit suicide and entered the reset elevator. Resetting means going back to childhood. Resetting requires killing the summoned self. The self here refers to the children and children who have been told everything by their grandmother after their amnesia. Why reincarnation? Because the dead guy who cut the child who didn't know anything with a knife (the one who pressed the elevator) was the one who was reincarnated and told everything by grandma. The rebirth is a child who knows nothing (has a memory), so he tried his best to prevent the tragedy of being sent to his grandmother's house, but it happened later (here I think the mother's transformation is still related to that strange uncle). Then he went back to the elevator, expecting another reincarnation, so he said I couldn't just go out, and he must get his happy life back (I guess he didn't know until his grandmother told him about the reset). But he didn't know that the one who was killed would be reborn (because the memory was erased and instilled by his grandmother), so the child who knew nothing was reborn. Story cycle.

..... that's probably it. ...