#part of why i'm so passionate about this is that this very phenomenon in kh inspired a HUGE chunk of the worldbuilding

[bluerosesburnblue]

You’re bringing up genetics, but genetics has never been a factor in Kingdom Hearts beyond one possible instance of an identical great-something-grandson that hasn’t even been confirmed yet. I think it’s safe to say that genetics and the construction of bodies as we know them is simply a non-factor in Kingdom Hearts canon, as much more emphasis is placed on the idea of the vessel attempting to match the contents. Terra’s genetic phenotype doesn’t change from “brown-hair” to “silver-hair” once Xehanort possesses him because that’s not how genetics works. It can’t just flip between the genetic coding that’s expressed that the original has no predisposition to on a whim, so I find any mention of genetics in the context of Kingdom Hearts to be completely inappropriate. It’s a fictional world that clearly doesn’t follow our world’s rules exactly, so you can’t use our world’s logic to argue if it’s possible

Aqua’s comment about Sora also comes after making a comparison between Terra and Riku’s disposition—there I’m arguing that she was referring to this for Sora as well, as opposed to the physical trait.

Fair enough, but it doesn’t change Xemnas’s comparison to Roxas which all but confirms that they should look almost identical, in contradiction to your claim otherwise below that:

I don’t even really see a definitive resemblance between the two [+Roxas to Sora] anymore outside of what could be understood even in real life between two unrelated people.

That’s probably the point that I should have highlighted, but the gist I got was that Aqua’s comparison wasn’t more likely about their personality, therefore there was no mention of a physical similarity between them, and thus it doesn’t exist

If we were going further than this route, I would only consider it plausible [if in being in the cards of being offered now] if there was a point of conflict where Sora wasn’t physically representing himself naturally.

I actually did think of this, and my mind went to Yozora. Perhaps it hasn’t been brought up in the current arc because it’s had no reason to be, but it may be in the future

“No, this isn’t the real world, and I am here. But this isn’t what I really look like. How’d you recognize me as Yozora?”

...

“Why are you using Sora’s name?”

There’s clearly something going on with appearances in the Yozora storyline that will be expanded on in the future, so I, personally, think it’s way too early to say that it’s “unlikely” that Ven had any influence on Sora’s appearance or that it won’t be brought up again. Especially since Ven is still an active player in KHUx and will likely continue to be so in the future of the series thanks to that. Nomura is wont to pull in things from way earlier in the series and give them meaning later (i.e. Xigbar/Luxu, the Ark/Lifeboat pod room in KH1). I’m not willing to take the explanation that Ven influenced Sora’s appearance completely off the table until the series is done and Nomura can’t come up with more explanations

I wasn’t even arguing if it was more or less likely that Sora was influenced by Ven than whether it was simply due to out-of-universe reasons to make the comparisons between them more obvious and they had nothing to do with each other. I just said that there was precedent in the canon for it to possibly be true and that I liked the idea as an in-universe explanation in lieu of any official confirmation because of that, not that it was particularly “reasonable” to be or end up as canon over the alternative. Maybe it’ll never be brought up again in the series. Maybe it will. I don’t know, the only real example we have to work with right now is Xehanort and the fact that Xemnas and some of the Organization had gold eyes, but with Xehanort it turned out to have an in-universe justification that bears similarities with what seems to be the case between Sora and Ven

You’re also drawing a distinct line between “Replicas” and “characters created from others” and “real people,” which is fair, but not the way that you’re splitting them by lumping Replicas in with characters like Roxas (and other Nobodies). Replicas are blank-slate bodies designed to easily be able to change shape to match the heart inside. Fact. But Roxas is not a Replica. He’s Sora’s actual body and soul under the influence of Ven’s heart. Remove Sora’s heart and whatever sense of identity it has, and his body naturally morphs to the appearance of the only heart inside it at the time. Roxas is the living proof that bodies in KH will change appearance to match the heart within, or at least what the heart determines its appearance to be. Every other Nobody retains the exact appearance of their original selves due to the complete absence of a heart. Roxas does not. Roxas is Sora’s flesh and blood physical form that morphed to completely become Ven’s appearance. This is a fact

Genetics has very little effect on the form of the body in Kingdom Hearts and has never been mentioned in the series, yet there’s plenty of evidence to point towards bodies morphing to match what whatever’s inside them identifies as. After all, what about the non-Organization Nobodies, like Dusks? Bodies and souls that lack hearts and memories that could shape their appearance. They become unidentifiable, shapeless entities

This even makes sense with Terra-Xehanort. Terra’s heart wasn’t ejected when Xehanort took possession, the end result has similarities to both in appearance, which is carried onto the entities derived from that. Xehanort’s vessels slowly morph over time as more of them are taken over by Xehanort’s heart fragments, but their original sense of self still has primary hold of their appearance. It just makes sense with what we’re shown that any heart within another’s body has some effect on the body’s appearance, no matter how subtle

If Ven’s heart had no influence on Sora’s appearance, it then begs the question of “why?” Why would this principle hold true for all of Xehanort’s vessels and Sora’s body when Sora’s heart is removed, but not Sora’s body before then?

And why is it more reasonable to assume that two completely different people just happen to look almost identical, knowing the above bits of worldbuilding, than the possibility that there might be more to it?

When I first learned of Roxas I thought he was meant to be identical to Sora, save for his hair. But then BbS told us that Ventus had a much larger impact on Roxas's appearance. I accepted this and more or less convinced myself that the two blonds did not resemble Sora much. That is until I watched BbS last month. When Aqua said that Sora was the spitting image of Ventus I was honestly surprised. Now I wonder why these two boys born more than a century apart would resemble one another.

Maybe when Ventus's heart connected with the newborn Sora, this influenced the younger boy's appearance in some way. That is to say, maybe Sora was going to grow up to look another way, but then Ventus came along and changed that somehow? Or maybe their similar appearance is the result of mere chance? Or maybe the creators will explain this in some unexpected way. What do you think? 

I think it’s certainly possible that Sora’s connection to Ventus did effect his appearance in a number of ways, and out of every possibility that one seems the most likely to me. There’s actually a strong precedent for the body changing to match the appearance of the heart(s) inside in the series

Take Xehanort and the characters that he possesses, for example. Over time, their appearance changes to match Xehanort’s own, with hair color, eye color, and/or skin color all morphing to match Xehanort’s and several characters developing his pointed ears.

Different characters show different traits, notably Terra, who had Xehanort’s entire heart placed into him, immediately developed the golden eyes and silver hair, and later developing the ears as Terra-Xehanort lacks them, but Apprentice Xehanort has them pointed, with his skintone eventually being such a subtle shade darker than Terra’s that it’s almost unnoticeable, and certainly not that close to the original Xehanort’s:

Source: [Discussion] Xehanort's Eyes by Dasaniiii on r/KingdomHearts

Then it seems to eventually get a little darker over time if Xemnas is any indication, getting to be closer to Xehanort’s:

At least for their depictions in KH3, which clearly shows Xemnas (who is Terra’ body) as having the same skintone as both original Xehanorts, but Terra-Xehanort retains Terra’s skintone

Meanwhile, Xigbar/Braig, who only received a fragment of Xehanort’s heart and not the whole thing at once, seems to have gotten the golden eyes and pointed ears instantly, developed silver streaks in his hair later (which could be age, who knows), and everything else remains unchanged. Saix has the same happen to him, minus the silver hair, over an unknown timeframe, and the rest all get the golden eyes but not much more. So it seems like overall: the presence of another heart, or even a fragment of another heart, begins to change the appearance of a person to match that of the heart(s) inside them, but the exact traits that change vary based on numerous factors, and more may develop over time

This can also apply to mere connections between hearts, rather than a heart physically being in a new body, if Xion is any indication as her appearance was shaped by Sora’s connection to Kairi despite her original intent being to copy Roxas’s and Sora’s abilities which allowed her heart to develop its own identity based off of all three of them that her Replica body generally takes the form of. I’ve also seen it theorized that Naminé’s blonde hair could be a remnant of Ven’s heart being inside Sora’s body during her creation, and I don’t think that’s a bad explanation for it (though it’s never been stated to be canon as far as I know)

This puts the appearances of Sora, Ven, Roxas, and Vanitas in an interesting light if you apply what happens to Xehanort to them. Sora’s heart has been connected to Ven’s since it was born, but he didn’t have Ventus’s heart inside of him until he was four years old, after Aqua called him the “spitting image of Ven.” So if his appearance was influenced by Ven’s, it had to come from that initial connection and not when Ven’s heart sought full refuge in Sora’s. I think it’s entirely possible that Ven shaped Sora’s appearance, but because it was only via a connection of their hearts at first, Sora was able to retain some of his own, original look (particularly his hair). Though, I’d say that it’s unclear if obtaining Ven’s full heart had or would have had any further effect on Sora’s body once it ended up there

There’s two big differences between Ven and Sora, and Xehanort and Terra. The first is that Xehanort took conscious control of the body he was residing in while forcing its original owner down, while Ven allowed Sora to be in control the entire time and fell into sleep in his heart. The second is that Sora and Ven’s connection happened when Sora was young enough that he didn’t really have a sense of self, while Terra was possessed at the age of what Nomura said was “about 20.” Either one of these could have had some impact between the differences between the two scenarios, as Xehanort’s possession usually caused superficial changes to the host’s body, while this possible connection between Sora and Ven allowed Sora to retain superficial characteristics but would have changed nearly everything else, like facial structure and physique

It could be that Ven’s connection to Sora’s heart caused Sora’s heart to develop similarly to Ven’s (like the Xion example above), which caused his “natural” appearance to develop based on what his heart identified itself as based on that bond

Ultimately, I can’t say for certain that Ventus had an impact on Sora’s appearance, but since there seems to be a good deal of evidence supporting that it would be possible, it’s one of the better explanations in my opinion. At the very least, the body being mutable based on the hearts influencing it is canon, so I don’t think it’s that much of a stretch to conclude that it’s involved with the reason that Sora grew to look like Ven, even if the specifics are unknown right now