At first I thought Satou was being a dick, taking advantage of Fukko's seemingly meek nature ... until we see how the dominant position gets reversed, once her "switch gets flipped". And by the close, we learn the underlying reason for it (no spoilers - read the story).
Conclusion (at least IMHO): "Perfectly balanced, as all things should be."
From the rooftop blowjob I assumed he was doing it for her. I assume his jerk attitude was from constantly being asked to do "favors" for her. He feels put out and responds with an aggressive attitude in the hope that she stops asking him. He truly cares about her, but probably want to be seen as more than a living dildo.
Nah, he's annoyed because he thinks he doesn't mean anything to her and is worried she'll settle for someone else whenever she's horny. Not that he wants her to stop asking him.
Heh, what a 'twist' at that ending. At first he gives off the impression like he's perhaps taking advantage of her, but later it's revealed that...Well, she was the one asking for it every time. I guess in that sense we're like her friends, first we judge him based on how things seem to be, but then we ding out it isn't actually the case later on.
That ending though. Well hey, I wouldn't say it's such a bad thing that she only gets horny around you. In fact, that is a very good thing indeed.
Oh man that uno reverse femdom was GLORIOUS. A lovely vanilla story to add to the collection, hardass MCs with good hearts are hard to come by these days.
No wonder Bakugo is always so angry? ¯\_(ツ)_/¯