I looooove stories that are this messed up. I think it's perfect as a oneshot, but I wouldn't be mad if this turned into a series!
I do feel bad for Shimamoto to have hated herself so much that she wanted all traces of her former self gone and didn't even see herself as human beforehand. That level self-hatred usually doesn't just appear out of nowhere. (I actually think her past self is really cute too, and I'm glad we caught a glimpse of what she would've looked like as an adult on page 22.)
As others have said, the creepiness on her part comes in specifically with wanting to look exactly like someone else.
Speaking of creepy, if Shimamoto went so far as to move away to where no one would know her, then I get the feeling that Shiratori didn't really "just so happen" to be transferred there after all, but I could be wrong.
