I'm not into ecchi so i thought the same but I like the main character and after I kept reading Nina becomes quite the "supporting" character and her character development is nice, she goes from dumb girl with big boobs to hard working-naive big boob girl, so if you dropped it, you are missing out the real deal just because you got caught on a lame start
Well..... a major spoiler
Nina will be a traitor as someone below said..... after being an ally for more than 150 chapters in the novel. Well, I would call it a terrible writing by the author. The author is too fickle. Too many plot holes and contradiction. Things just pop up randomly without explanation. The story turned abruptly. And it got worse, really. Bware of lots of tragedy and ntr. I wish the manga has a different story than the novel though. Otherwise, it’s not worth it.

just started reading this and stopped at ch 4 to release my emotions. the girl with ginormous boobs forcing the kid to be friends with her pisses me off :( feels like she was created only for the sake of being annoying and to serve as fanservice