Reiji’s dead magical girl body seems to be the one from page 3 of chapter 1. I am excited to see why Rin committed a seeming murder and why it relates to being a magical girl.
My working guess is that I think Rin’s obsession will end up being with staying a magical girl (at all cost) since so far we haven’t seen a hint of anyone else in his life.
We’re not really getting a lot from these three chapters though, so it’s a matter of waiting for more information.