Its not a tape, this ain't the 90s. Based on her story she's not even the origin of the video. Beating her up would be kind of an empty threat since, while it would hurt her it wouldn't stop the footage or anything. I'm not 100% sure why Misora is hiding their relationship. It could just be embarrassing for her or she's worried it'd effect her career or rumors about her being actually gay (rather than bi) would surface. Since I don't know her motivation I can't know why being found out is a big deal at all.And in the end, what stopped Misora from just scaring that girl by pretending that she would beat the shit out of her if she didn't return the tape to her and stop the blackmail?