Dilandau Albatou

A mentally unstable pyromaniac with a bizarre and shocking past, Dilandau is the tactically ineffective commander of the Zaibach empire's elite Dragonslayer's unit. Diandau takes no prisoners, and burns towns to the ground with little provocation. After being wounded in a sword-duel with Van Fanel, Dilandau becomes fixated upon him, and places vengeance over all other objectives (with as much fire and collateral damage as possible, of course). It's revealed later in the series that Dilandau is the result of Zaibach's experimentation on Allen Schezar's sister, Celena. When Celena was abducted by Zaibach, they used her to test their "fate altering machine", which changed her fate to become Dilandau.

After having a mental breakdown, the fate tampering on Dilandau's body begins to come undone, and he's sent back to Zaibach to be fixed. After Allen discovers the truth about Dilandau, he's able to convince Dliandau to stop resisting his true fate as Allen's sister, and he permanently becomes Celena.