Finally I got it! This is a daring subversion of the "returner" genre, only this time instead of a young body the MC gets to keep their body. This is done to shine a light on this pervasive genre and make us, the readers, realize just how disgusting and manipulative this theme is.
Just think, normally this would be a "teenager" doing it to another teenager, and as such, visually we would have no problem with it! In this case however, we see it for what it is and quite a few people suddenly have a problem with it.