Really fun read, enjoyed experimenting with the choices and seeing all the different endings! I almost missed that the title screen changes depending on what you do, its very subtle but a really cool effect! I'm not sure if I managed to see every version of each ending, as there seems to be small variations depending on choices, but I did get the secret ending, so that was fun, haha!
Unless I missed something, it felt like the plot with the uncle and dad doesn't really go anywhere, which is a little bit of a shame, but I get the focus is on the possession and Callum's story more than that.
Minor nitpicks aside, I had a lot of fun with this VN, and I'd love to see what you come up with in the future!