I don't quite understand the 5th story can someone explain?
Looks like Momiji is in the after life and Aya wants to get there but cannot. Only a feather crossed over, and Momiji welcomes it as if it were Aya. "Welcome back" might have been better as "good to see you again"
To me it looks like aya dies as well (since you see her falling down).
This is why her feather appears in the afterlife
I really think this manga should be separated in two, the two stories are so different from each other.
(Also what the hell? Yukari please don't use your niece as a body pillow)
Keine is also considerably older than Udonge at the time of the games, as far as I know. So her dying earlier makes sense. And, well, accidents happen.
According to the wiki, keine is 60 but udonge is about 200, maybe the data there is wrong