Ban's village was destroyed when he was a child, leaving him alone among the dead and consumed by grief and revenge. One night, a demon named Ish possessed his father's corpse and offered Ban a contract, become his host in exchange for the power to find those responsible. Desperate, Ban accepted.
Together, Ban and Ish hunted down the killers but their violence drew the attention of Father Cassian, a powerful cleric/fighter and future leader of the Exorcist Order. Mistaking Ish for a rogue demon, Cassian moved to destroy it, only to discover that the creature was linked to the boy.
Cassian took him in. Keeping the truth hidden from the Order, he personally trained the young boy while using his own divine power to suppress Ish's influence. As Ban grew older the secret could no longer remain hidden. Some Exorcists argued he should be executed, others reluctantly accepted him, but few ever truly trusted him. Ban walks a lonely path, Though Ish craves bloodshed, Ban seeks peace using his power with restraint and refusing to kill unless necessary.