MC and Senpai aren't compatible. She's physically abusive, forces her niche interest on those who can't handle it and seems to only be chasing him because she's afraid of losing him knowing full well he likes someone else and their feelings are mutual.
Honestly she needs a smack over the back of her head and to be pointed out that she's being a fuckwit.
The gag physical violence aside, this isn't uncommon.
People don't
play fair just because someone else likes someone else. She decided she wanted to keep him around, and so she's using the weapons at her disposal.
The least realistic part of this scenario is that, being a manga, she won't be successful. In real life, guys are typically dense and/or horny enough that if a girl like that threw herself at him he'd just go along with it.