He...Ran away? Rather than take responsibility?
A few minus points right from the start, but as for her, she never gave up, even after two years and finding out he has a girlfriend.
That perseverance seemingly paid off, I suppose. He started neglecting his girlfriend in favour of her, and in the end she broke up with him, leaving the spot next to him...open.
This man is a sexual predator for sure. That's the controversial (maybe) should not be controversial take, right from the start. Teachers should not prey on their students. This story does a good job of showing us the conscience of Kishikawa. You will not write him off because he is self aware. He feels shame for what he did. Later he finds he is a slave to the young girl's body. No one wants to be a slave to anything and be aware of it. I feel Kishikawa is a tormented character. His past will not let him go. It is easy to read a happy ending. Scratching a little deeper gives us a little perspective on another message in the story.
I can't tell if you think it was a happy ending or if you're pointing out it's better to read a story like this than a happy ending...If you thought it was a happy ending, yeah, things worked out for the female MC...But the girlfriend got crapped on, so the ending overall wasn't a feel-good moment IMO. It was just a tale of two individuals that couldn't let the past go (slave to whatever or not), even at the expense of hurting a partner (seeing the gf walking away dejected completely took away any empathy towards the two lovers). Neither two are great human beings, so the ending wasn't a credible "ride into the sunset" fuzzy feeling.