History (anime version)
Eizen was first seen in the eighth episode when Sorey decided to investigate dragons after one attacked the city of Ladylake. He was fighting against his sister Edna, who was trying to stop him from causing damage without killing him, when Shepherd Sorey appeared, and tried to purify him, only to be told that someone who had been so corrupted as to become a dragon cannot be turned back. Nevertheless, the two battled extensively until the intervention of another seraph named Zaveid, who fired magic bullets at the creature, all of which it dodged, despite its immense size. After escaping from Eizen, Edna later admitted to Sorey that she had spent years searching and searching for a cure for her brother, only to find nothing, and concluded that her brother would almost certainly have to be killed. Nevertheless, Sorey promised that he would find a way to save Eizen, despite her disbelief. While Eizen and Zaveid continued to battle, Eizen wielding fire, Zaveid using magic bullets, Zaveid cursed Eizen for losing all of his memories of who he was and everything left of his former self. To protect Zaveid, Sorey took in Lailah’s powers and entered his Shepherd form before using his fire-sword to attack Eizen, dealing several blows, but being careful to avoid fatally injuring him, all while Edna watched on in horror, flashing back to the man he had once been. However, eventually Eizen slammed Sorey into a cliff using his tail before issuing a triumphant roar.Edna then tried to talk to Eizen and break through to him, standing on a rocky platform, against Zaveid’s pleas. Eizen reacted to her presence by kicking the rock, smashing it, and throwing his sister into the air. He then turned his head towards the still airborne Edna and began to produce flames from his mouth. Sorey was able to collect enough strength to leap into the sky and catch the falling Edna, and while he had planned to lay another strike on Eizen, the moment Eizen’s eyes connected with Edna’s, he recognised her as his sister, stopped emitting fire, and flew away into the sky.
Edna then made a Sub-Lord Pact with Sorey in order to lend him her seraph powers during future battles, and to better help him find a way to save Eizen.
Sorey was finally given hope that he would be able to purify Eizen when he successfully purified another large dragon which attacked the city of Ladylake by spreading its Malevolence into both himself and his squires, Alisha and Rose.
Eizen was not cured by the end of the series however, since Sorey became trapped deep within the earth on a quest to purify Heldalf in an act of self-sacrifice, and in the second half of the final episode, a few years seem to have passed (based on the apparent age of Alisha), and the world’s Malevolence level was continually dropping because of Sorey’s actions, and the actions of his successor as Shepherd. Due to this, Eizen’s mind gradually restored itself and he regained his ability to reason, think and speak, once again becoming a close brother to Edna.