My guess (and I really hope this isn't right) is that it's going to tie into the gacha game, Higurashi Mei. As for an explanation and a motive, I really want something that can explain this other than witches and Umineko references.
There's this one Italian mega autist on /a/ and /jp/ who has the worst possible theories about Higurashi and Umineko who was throughly blown the fuck out by this episode's reveal since he thought Rika and Ooishi were the culprits. He literally writes fucking manifestos about his retarded theories that make no sense and it's a pretty interesting rabbit hole if you have read Umineko and Higurashi into how somebody can be so wrong about a mystery.
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