Ending kinda underwhelming, would have made it better if they had sex for real and Mikoto disappeared like how it was written, then Sayuri learned about what happened to her actually, and Mikoto dies in the end. That would leave a deeper image of Mikoto in Sayuri's life, and make an epilogue depicting Sayuri finally leanred how to move on and socialize/finding her love.
Also dad's backstory is kinda shit. He abandoned her, with no contact whatsoever. That's literally abandoning her.
Overall, the story is extremely good, with very great depth on Sayuri and Oga's characters. Wish they'd expand more on Oga's relationship with Himeko though, gotta get that yuri on. Just a little lackluster towards the end with the yandere and the ending. Short but good read nevertheless.