Lastly, Sensei: the mansion, if you notice is actually a prostitution house, cameras, magic mirror, handrails, and a lot more cameras. She was raped when she was young, sold to prostitution, and rose from the ashes, won't be talking about the details but Sensei's life is one of the tragic stories in the novel
So if you're going to talk about the MC being just perverted, You're wrong, you've never seen his character at all, you've never known his past, you've never seen him get molded with every events, turn from a very passive ignorant child to a responsible and gentle man.
If you think the girl's so naive, yes, she's delusional, prideful, and selfish. You will be asking the same question other characters in the story ask, Why does he even like her? And that question is very well explained too, it's not some bullsh*t love at first sight, no no.