Xecir's the guy in black with the keyblade. Just sayin'.
Xecir is Eric's twin. He was stolen from his mother at birth and was given to a loving couple near the Destiny Islands. At 14, Xecir joined forces with the Heartless Repulsion Society, and taught himself to wield his keyblade, Bond Of Flame, in the process. He and his best friend Alphren died while holding back a massive wave of Heartless. However, Death took pity, on the now 16 year old Xecir, and gave him his life back. A side effect from this process is Xecir's eyes look dead.
Xecir is proficient in Fire and Wind magic, slightly contrasting Eric, who wields Water and Wind magic. Xecir's personality after his resurrection is slightly cold and uncaring, but that's because he's an anti-hero.
He also represents the douche in me.