My own thought is that this is hundreds of years in the future, with Alice finally passing away (although not having visibly aged since she's a youkai) and finally reuniting with the spirit of her beloved Marisa.
This is how it's implied but the dialog makes no sense if it's taken that way since it would be Marisa waiting on Alice not the other way around.
Also the end of chapter 4.5 seems off. That seems a fairly serious conversation and the conclusion to it really doesn't even seem to be hinted at. Marisa seems actually mad at Alice and just storms off then the chapter ends and we jump from there to the end of Marisa's life.
And speaking of things that should have been dealt with directly (especially since it's never even hinted at) is the whole thing with Reimu and Marisa. When Marisa comes back to Alice's house after being thrown out, Alice never brings up the topic for discussion. Though in my opinion coming to Alice for that discussion was dumb of Marisa in the first place. She admits to being aware of Alice's feelings but she doesn't stop to think how what she's saying sounds.
Overall it was an interesting Touhou doujin but not my favorite and definitely has some issues. (That title would belong to Liar shortly followed by A Slip of the Tongue.) It had some nice art though.