Revo already introduced her, but here is some more love for the redheaded Kairi. She is the original Kairi. And that should be appreciated.
So why is Kairi a great waifu?
She's brave, despite often being portrayed as a damsel in distress - which is an excellent waifu quality in itself. She is not the strongest fighter, but still a fiery lady. Kairi puts herself out there if given the chance. She'd do anything to protect her loved ones.
She's a good and kind friend. Seeing how well she treats her friends - and not only the people she's known for years - it's a sign of how well she'd treat you. She's a friendly, positive person. Great to be around I'd say.
She also enjoys long walks on the beach and watching the sunset together
So if you think about it, there is only one option in here. Nothing can beat a redhead