Fully expected Tragedy
. I'm glad to just have been misled.
... How could someone interpret this as involving Mokou outliving Keine when it literally starts with Mokou panicking over the possibility that Keine had found a certain box?
Probably because she doesn't appear for most of the story, except in flashbacks. In fact, aside from a very brief scene, most of the story is Mokou chosing to moonview alone with her mementos of Keine while fondly remembering their moments together. I think it's fairly understandable how people can be misled by the mood.