Controversial Opinion:
I don't like the ending. I think it goes against the themes of the work and the concept built up to thus far. I genuinely would have preferred if we never got a reveal for the bride and it was left ambiguous because it doesn't matter. The point of the novel was always about the characters, their struggles and their relationships to one another. I think giving us a clear-cut ending undermines that as it removes the idea that each of the characters has their own reasons for liking one another. They're each five parts of the whole and it could be anyone of them. The use of ambiguity would have been better as it would have allowed us to more thoroughly analyzed each character's relationship with one another, given us reason to more deeply look into them and why they may have fallen for Fuu, but this way kinda just resolves it which is less interesting.
The the core messages thus far have been about family and the girls in how they interact with one another, the struggles of working together as a family and how it relates. It's nothing against Yotsuba, though I think they could have been developed a BIT more for one another personally, but the beauty of it possibly being anyone is that it gives that core family aspect and only knowing who each girl is when you grow to love them more depth. We, the audience, don't love the girls, we're merely outside observers. It would have been stronger if only the characters knew and we were left to guess for ourselves, deduce based on context clues, how they address and speak to one another and hints in the story, but no clear answer.
I previously have said that I thought the ending would be a harem ending, not because I thought it would be better, but because I thought such an ending had more build-up. Make no mistake, whilst I think that would have been cheap, it still would have been more textually and thematically consistent than this. This ending I feel is a bit unsatisfying, as I think it makes the novel too plain. If you were to get spoiled, most of the books would be weakened and re-reading it would be less entertaining and charming. You lose out on the constant guess of "who will it be?" or "who will he choose?" Now, you won't watch the other four characters as closely as they grow to love Fuu because there's no point. It's a shame, but it weakens the literary merit and story of the novel. I am a strong proponent that such core questions, such forefront ideas of a work should never be answered in a work, but be built up, expanded upon, and developed to the point where the audience draws their OWN conclusions. Some of my favorite pieces of fiction use ambiguity to convey their themes. Hamlet gives no clear answers, but only shows select, relevant scenes so you can piece together the key details. Invisible Man never explains its core metaphors or what will happen when the narrator comes up from his hiding. The Things They Carried never addresses questions like "Did O'Brien kill that man?" Because such important ideas and concepts are better left unanswered. Answering such questions in a story only makes it weaker, and this is a case where having a clear answer weakens the overall work in my eyes. It should have ended with him touching the door, jumping back to the wedding and having a shot only focusing on the Fuu's sister, father, and the girls' adopted father, hammering the theme of family and the importance of it and how it ties people together, before ending.
Works are better in my opinion when not every question is answered, but deliberately so. Not in such a way to cause plot-holes or to leave important exposition out of the hands of the audience, but that each member can have their own interpretations that validate that perspective and facilitate further discussion and literary dissection of that work. I definitely think that it weakens the entire series overall for this, and that because of it, a once beautiful story that could be analyzed, dissected, and discussed as a great piece of fiction gets ruined a bit because of the core message being defied and a definitive, objective and in-text piece of fiction reveals the truth for us. It's a shame, really, because once such a question is answered, I don't think rereading, interpreting, or discussing the core themes, ideas, and complex character interactions will be NEARLY as compelling or frequent as they once were. If you had gone into this manga and someone told you "it's the girl with the bunny ears," I think that would ruin the experience. And I don't think I can read this manga again because of it.
This is not to say the manga is bad, it's still one of the best mangas out there and I thoroughly enjoyed and was entertained by what I got. I just think the ending weakens it significantly and that a good author knows what to reveal and what to keep vague, as storytelling is just as much as what you don't show as what you do.
I know I will get shit for this, but I feel like it deserves to be said.