@Stadenwick, blackmailing Ishigami? WTF? This can't be called blackmailing, she didn't threaten him or anything like that. He is doing all of this on his own accord, because he feels guilty and grateful for saving him.
Calling her manipulative is BS. She has a strange personality, and she isn't always sincere, but she cares about him genuinely. She clearly felt something bad could happen, and followed him to the stairs, if that's not a proof of her feelings, what is? Not sure if she likes him in a romantic way, but he is like an annoying older brother to her, if anything: she criticizes him constantly and makes fun of him, but he is still very dear to her.
As for Tsubame, she is also not as bad as people make her. Popular people thots and whatnot is just a trend today, I get it, but she didn't do anything to deserve it. She clearly has some feelings for him, but she isn't sure whether she can start a serious relationship with someone, so she wanted to at least share some intimate time with the person she likes, and thought that at least it would make him happy. Of course it was a stupid decision on her part, but everyone makes mistakes. And after what has happened, her feeling for him will only grow stringers, since now she can clearly see that he isn't just after her body. If it was the case, he obviously wouldn't stop himself there. So yeah, now that she knows that for sure, it wouldn't be surprising if she falls for him hard (and we can already see signs of that happening in this chapter).
Really interested to see how it will turn out in the end.