i'm not sure.. but isn't "Past Heaven" the sequel of this? coz same characters and all :3
Agreed basically, however their characters become somewhat different.
(Or rather I'd consider them two separate oneshots with coincidentally similar character names and designs, since their personalities changed so much.)
I don't agree at all, the characters seem the same to me. Ayumu is still gregarious but it's revealed it's all just a front. Yuu is very confused about all these new things she's feeling & experiencing, but she's trying to come to terms with how close she feels to Ayumu all of a sudden. I don't think either is acting out of character, they're just showing sides they didn't show in the first chapter.
Anyway, I came here to mention how awesome I think the grandpa is. That guy rocks.