She probably couldn't, the arena they were in was her guard. If anything, it may be a continuity acknowledgement as she didn't even block with her keyblade when Vanitas attacked her.
Sora and Kairi really isn't forced, I don't see why you think that. She loved Sora from near the beginning, they're childhood friends. He was her safe space when her heart was under attack. She lived those moments with him and he brought her back. He marked the wall with sharing a paopu fruit. He didn't expect her to see it. Then she saw it, was happy that he seemed to like her back, and she put hers up too. Then they unite again in KH2 under duress and after finally uniting again (he focused on Kairi as soon as he heard she was also captured) he went back to focusing on Riku because he sees the trinity while she sees Sora and his loyalty to friendship. She helps Sora reunite with Riku so she can hopefully get back home with him. Then they meet back up again and they take hands. He notices that she also marked the wall and there's no telling what else happened off screen (discussion of romance etc) but I think something definitely did happen to cause her to want to fight alongside Sora. She tried to train hard to save him from shouldering this burden all on his own, however destiny chose Sora and he couldn't break free from those chains. It is clearly evident that she loved him and he loved her because when Xehanort destroyed her his response was "Why her?" he knew it could have been anyone and he may not have fought as hard, Xehanort hit Sora where he knew it would hurt. This romance has been building since moment one in KH and has never once been forced. From the moment she suggested they leave without Riku, and Riku knew it too from the moment he offered to have Sora share a paopu and threatened to be the one to share it with the race.
Don't get me wrong. I'm not saying people can't like SoKai? And I mean, yes, there is in-game evidence that they are close, that's indisputable. My problem is how much it is hammered in by OTHER characters and how much the ship is prioritized over Kairi as an actual character throughout the series. I mean, everything you listed is all fine and dandy, but... how often has Kairi been shown having meaningful interactions with characters that aren't Sora? And actually shown, not just vague glimpses or being talked about.
We don't really get to SEE much of her friendship with Hayner's group. When she speaks with Roxas, it's about Sora. She has a few moments with Riku in KH2 that are nice but way too fleeting and a tiny bit in 2.8, but otherwise? There's very little. Nearly all of Kairi's screentime revolves around Sora, so you'll have to forgive me if I'm not enthralled by a ship where one party doesn't get to stand on her own outside the shipping context.
To me, having characters like Donald and Goofy constantly remind the audience of the ship during KH2, for example, just feels like a classic case of tell, don't show.
Here's the problem. Sora has plenty of time to be his own character with his own friendships and experiences. Kairi?
- Comatose through most of KH1.
- Offscreen or captured through most of KH2.
- Only vaguely mentioned in Days, barely acknowledged in Coded
- Brief moment in BBS with Aqua as a child
- Has some moments with Lea in KH3, and admittedly
it's cool that she's a party member during one of the endgame fights, and yet... we still don't see her have meaningful interactions with most of the cast, ESPECIALLY Riku, who is supposed to be one of her best friends, too.
Now do you see my problem with SoKai? I just don't think shipteasing automatically makes a ship compelling. If you like it, that's fine, but I just can't root for a ship where one half of the pair got the serious shaft in EVERYTHING that isn't her connection to Sora. That, and the ship just doesn't interest me (but it's fine if it interests you).
I just really think that if they were going to make the ship a thing... they should have done more with Kairi's character. Because they did not and she contributes so little to KH3's story, it just makes me mad when a noncanon manga has a much more well-rounded Kairi who ISN'T just there for shipping.
And again, it makes an even more glaring contrast with Xion and Aqua, who have strong bonds with both members of their respective trios AND get to go out and do their own things as their own characters. It really makes it feel like there isn't a true, strong trinity of friendship that was present in at least parts of KH1 and KH2 (but even then, I'd argue Kairi still didn't get much outside her scenes with Sora).
I just want Kairi to be more than Sora's love interest. :/ I wanna see more of her personal aspirations, her interests, etc, etc.