I know this is kinda off topic but why is SoKai better than Naruhina? Because Sora and Kairi always had a connection. Though Kairi isn't the strongest character, that doesn't stop her from trying. In fact she saved the world by saving Sora. Has Hinata done that? In fact Sakura saved the world by saving Naruto bunches of times.
Kairi has more of a point in the story and possibly lore of the series. She's also not useless and is there for Sora namely their hearts. Better portrayed in Kingdom Hearts than the bonds nonsense Naruto wouldn't shut up about hell Fairy Tail portrays the main message of bonds better than Naruto does. Also wasn't it Sora who brought Kairi to his island there fore saving her when Radient Garden fell. Hinata did jack kitten for naruto while Sakura did a lot more than her, One of the best Sora and Kairi moment was in the first game after you beat Riku for the second time and Sora unlocks his heart and her bringing him back after Sora turned into a heartless. I'd like to that happen in Naruto were Hinata tries that and it doesn't work but Sakura does it and it works. Hope Kingdom Hearts III has Kairi be a badass like Aqua is and she's playable. Good point Kairi tries her best to help Sora, When Hinata tries to help it makes the situation worse (Pain and Neji).