Question: why is xigbar half xehanort?
Answer: Half-Xehanort Braig later known as Xigbar and also Half-Xehanort was originally a minion of Master Xehanort who later became a nobody and minion of Xemnas. Xigbar retains Braig being a host for a piece of Xehanort's heart, though after being defeated by Sora, he becomes Braig again.