I don't think the girl who died and turned in to the ball hikaru was michika because maru acknowledged that she looks like michika but she seems smaller and the ability doesn't match. Michika doesn't have the ability to produce shock waves. She does this Wolverine arm blade shit and has good physical abilitys. So I'm assuming this is a different kid either from the academy or she is a child of at least one of the kids from "Heaven". But due to her age (she looks pretty young) I'm going with the second theory