Why in Kingdom Hearts 3 does Sora kairi and riku look like knights and there weapons r different

Firstly, it's not Kingdom Hearts 3, it's Kingdom Hearts: Birth by Sleep, made for the PSP console.
Secondly, they aren't Sora, Kairi and Riku - they're Ven, Aqua and Terra. Supposedly, they're counterparts to the three though and somehow linked to them.