For me it definitely took me some concentration to be able to figure out exactly what was going on, or maybe to confirm what I thought was. I didn't think it was written vaguely, just layered like a puzzle, so the reader had to do a little work.

It is very sad. I think it's the details of William that make it sad for me--here he seems like a real little person, rather than in several other fics I've read about him dying he doesn't have much personality beyond alien miracle baby.