I honestly just thought that the memories were replaced/added to when he was 7-8 years old, because he made that wish for himself I was going to think that ur theory of him being replaced by a different him might be correct but then where would the adult nine go? I don't like that he'll never see the same Melissa so I'm gonna stay blissful and think the memories were added for my sake
Yeah, I was worried about that, but quickly dismissed it - like I said, that's just one theory, after all, otherwise that would mean she's going to be a lot, lot older when they reunite. - My persisting theory that it was just a slight moment for little Nine, to grant his wish... adult Nine would return to take his place as he woke up in his real world.
What he thought was a dream, could very well be an alternate universe. The one thing jarring this pleasant thought is the fact that while there are several story universes, there's only one Melissa.
So, maybe, it's a "link". His young self's wish made it a possibility, his memories afterwards pushed him to move forward, wish granted, and wake up as adult Nine. He experienced a dream-like childhood with Melissa. A mix between dream and reality, youth and maturity.
The last sidestory(?) was a little confusing, but I think I can imagine what may have happened, maybe. Little 8 year old Nine wanted to meet someone warm, as he said somewhere here. He likely made that wish on a full moon, and hence it was granted - on the moment wherein there is no more danger nor crisis, and their feelings for each other are already clear and determined. If it happened earlier, Melissa might not have been able to give him all that much care due to dealing with crisis after crisis, not to mention how it might impact future Nine's relationship with Melissa. So, he likely replaced older Nine for a moment, until the magic wore off and he went back to his world. After that, little Nine was determined to meet her again - perhaps in a different timeframe, in a path that leads to a similar future? This is what confuses me. I don't think Melissa had to wait for this Nine to grow up, as old as she is, for them to reunite, when they were already together.
If it's an alternate story, universe, and timeline, then we can't guarantee if it's the same "Melissa" that this Nine will meet. So, maybe, little Nine reunited with another version of this reincarnated Melissa, outside of the usual story too, but in a different path? And then, in the previous world, adult nine must've simply thought of it as a strange dream, probably to be told that a younger him had played with everyone in there?