Help remember a manga

I can’t remember if it was shounen ai but I’m 85% certain it was. Anyway a boy moves into a house for some reason I’m remembering his room being in the attic. There’s a landline phone and it starts to ring. There’s a boy on the other line and they start to talk. That boy used to live in the house I think…. i don’t remember clearly. They become friends but in the end it turns out that the boy he is talking to is from a different time line? Or a parallel universe and he is either dead or someone he knows dies. So the mc tries to save him or someone else that boy knows in his universe by going to the school they may both go to?!? I don’t know I might be remembering the ending totally wrong but I know for sure they talked over the phone and that it turns out there was some type of magic/fantasy tied to it. Also random but the author I’m pretty sure is a guy and he said this was the first BL he had ever made. So it’s not by a popular/prolific BL author.