Clearly the paopu is not automatically proof of romance. It always, ALWAYS depends on context. In kh1 Sora (and the audience) is told about the legend of the paopu. Selphie thinks it’s very romantic. Riku doesn’t say but it’s pretty obviously implied. -
Whether you believe Sora’s feelings for K in kh1-kh2 are comphet or a real crush, the paopu is framed as something romantic. People think sorikus deny this. We don’t. The full picture is important. So, we can say Sora almost definitely viewed the paopu as a romantic thing.
Then we get to BBS, and another view of the paopu is shown to us. Aqua states that the fruit represents an unbreakable connection and makes charms for her friends inspired by it.
So, now we know the paopu doesn’t /have/ to be romantic. But, at this point Sora still views it that way right? Next we see the paopu as the keychain of Sora and Riku’s combined keyblade. While it’s not proof of romance, the context of it is well, it’s /something/-
Sora and Riku have just created the song Dearly Beloved together and have been told that their hearts are always in tune so they’re free to sing, that they are always holding onto a little part of the other. Forgive me, I find that to be pretty romantic...but I digress
Anyway, so then we come to the paopu scene. The big romantic moment everyone has been waiting for. Sora is going to share a paopu with K just like he wanted to in kh1. He still believes the paopu is romantic, it’s all set up- a perfect sunset right before the final battle.-
And....right from the get-go, something is off about the scene. Instead of paying attention to K, Sora is distracted worrying about Riku being alone. Sora has no plans himself to take this opportunity to share a paopu with K. She is the one that initiates, to his shock.
He is not happily surprised, not shyly flustered as one would expect. He just looks at her in confusion, sadness, seriousness. His body leans uncomfortably away, eyes dart around, he opens his mouth but doesn’t know what to say. So he just looks to her to explain.
Why does he react this way, if he believes the paopu is romantic?
Well, that’s the exact reason. To him it was romantic and now he has realized that he doesn’t understand romantic feelings. Whatever he felt about K, he doesn’t anymore but doesn’t know how to deal with it.
Well, that’s the exact reason. To him it was romantic and now he has realized that he doesn’t understand romantic feelings. Whatever he felt about K, he doesn’t anymore but doesn’t know how to deal with it.