Why didn’t she slap the other guy too when he raped her multiple times??

This idiot phantasy in this kind of genre where the girl doesn't want it, but definitely want it.

You might be new here. I definitely agree but everyone has erased that part of the story so that we can have a better story.

Think of it thus way, that was an alternate universe where bad koichi raped her and smart noto reported him to the police and was arrested. The end.
Then we have our current story, where its a nice office romance as well as next door neighbors.

So much better(●￣(ｴ)￣●)