Just a little side note, something I saw pointed out recently that seems to apply here. When sending a message to non-English speaking authors, try to avoid English idioms as much as possible. There are a bunch of cases where artists think a comment is negative, or even upset at them, when it's actually a compliment like "Your stuff is so good, I hate it!" Better to keep it as straightforward as possible.
But what will happen after Misao dies? Will She become a ghost too and they both be together forever? Or she won't become a ghost and Mizuki will be alone for eternity. Alone in a whole world. Only precious memories wiil remain.
It's a great story, but too sad for me.
They've been bound together for a long time, and pretty deeply given their relationship. It's entirely possible that they both move on together afterwards.
I do like that there's absolutely no room to misunderstand right from the first chapter. It's not "I love you too" and both taking the other as meaning friendship, it's right there in the open. I can't think of a lot of series where they state their intentions so clearly at the start, all the more so from Morinaga.
Also, is it me or does the art look a little different from her norm? It seems similar to some of the more "pretty" parts of A Room For Two.