Am I the only one that read the train-jumping at the end as not entirely driven by shame and being followed by a creepy girl? To me it seemed there might be an element of the supernatural to that, like Rini was causing a Poe-like irrational panic, leading to his death so she could feed off him somehow.
And I hate to say this about such a dark story, but I was laughing my ass off for the first half, particularly during the bathroom scene and the date with "Daddy". "A panda who solicited men for money" was a great bit of characteristic description.
I think we need to ask: is Rini really happier at the end. She is no longer tormented by train perverts, but I imagine the girl from the beginning of the story would be horrified by the end worse than any of us outside observers. Her personal change isn't just scary from a gender-politics perspective, it is scary because she seems to have lost herself. Is she really any more free than she was at the beginning, or is she just blinding following her mother's lead? It almost reads like a possession story, she is changing, becoming someone totally alien and it isn't clear that she has any real choice in the matter, other than the initial choice to not walk out of that bathroom.
On one hand, the shy girl would have lost her innocence and ended up an extremely damaged person when her uncle inevitably molested her, on the other, when she starts taking joy in killing perverts she is certainly no longer innocent, and maybe not any less damaged. She completely avoids the middle ground as ElectricPaladin points out. Is the horror maybe that she is happy with her murderous predatory existence?
I definitely liked the story, and rabbit spirits are an under-represented monster-minority; it's nice to get a story that truly makes them scary.
P.S. the foreshadowing hand-stab in class seems to indicate that her wrath is not limited to perverts, just generally aimed that way.