New girl Neko Fujinomiya is this show's haitenai girl. She claims feeling "moderately tense" is healthy. Well, it raised Masamune's blood pressure, so it's not healthy for other people.
Neko's overly familiar encounter with Masamune made Aki and Yoshino angry at his careless reaction.
Aki didn't like this new girl Neko transferring in it at all. She's got a backstory with Masamune and she's not shy about being manipulative either.
This being a romantic comedy, it was pretty conventional to get Aki in a swimsuit and a near drowning event to force some dramatic intimacy. Oh well, nice butt.