I guess some people may have different opinions of what having a heart means. But in my opinion, actions are bigger proof of that than anything else. About what else is it like to have a heart... Have you ever felt as if you're in pain, but there's no actual wound in your body? For example, when you were told that you're not supposed to exist. What did you think then? Did you feel uncomfortable or wounded somewhere?

[There's a soft hum, and then a brief chuckle, "the only one", he says. Despite there clearly being two people who remember him.]

But Riku remembers you as well, don't you? If you really were never supposed to exist, if your existence was a mistake that eventually gets fixed like that. The normal thing would be that everyone would forget about you. Or that their memories would be replaced with Sora being in your place since it seems you're like a part of him or something.