I couldn't wait to do this costume! I think Kairi is just adorable in KH1. Too bad she's comatose for most of the game. I first started this cosplay in 2009 but never technically finished it until 2015.
The shirts are just stretchy material and bias tape. At the time I was short on materials, so the black tank top is actually 2 different fabrics lol. It'd pretty bad.
I had had the skirt fabric for years and had made the shorts and belt loop, but i never made the skirt flap till way later. I used a jersey knit and cheated on the scallops by not hemming them since jersey doesn't fray. The flowers are painted pretty clumsily with acrylics. The belt is covered by the same purple spandex as the bicep armband.
For the yellow armband, I used the same method as Lilybit at first then decided to split the cup holder thing and put fabric over it. I then whittled it down and messily closed up the fabric edges.
When I first wore this cosplay, I also made the shoes for it, but they got destroyed in a move and I never bothered to remake them.