Leo Demonheart

Leo Demonheart is the former hero who denounced by the human world after saving them from Demon Army because of his unparalled power. In Tokyo 2060, he was created by humans to fight back the demons. He is the strongest of all of the Twelve Demonheart Series. He is the titular male protagonist of Yuusha, Yamemasu series.

Appearance
Leo have deep red eyes and black hair.

Pre-Creation
Initially being created as a weapon by Humans to beforce against Demons coming to Human world by a hole, Leo got no emotional feelings other than killing the demons and protect the humankind. He used to be a silent guy and doesn't talk much. Among Twelve Demonheart Series, he is only one who wants to avoid useless resistance and uses violence unless the other party does.

After meeting a certain demon, he changes drastically. Leo befriends with him as being his first friend. The demon taught him about human feelings and how he should stop living on other orders that he should live for himself.

Post-Creation
As being the sole survivor among the Twelve Demonheart series, he gradually changed. Leo had gained a high ego for being a hero. Even after saving the mankind, he sticks to the mission of saving humans and that made him go to the demon world. From generations to generations, Leo has been proclaimed as "The Strongest Being". Undoubtfully, Leo had came to the conclusion that he has the hunger of being a hero and likely that because he get excited on killing someone.

As the times passed, Leo finally defeated the demon lord, Echidna, but that ends as a betrayal. Leo get denounced by humans because of his monstrous power. This happens to first time that Leo hold a deep grudge against humanity. Leo then get blinds in revenge that he wants to destroy the whole world that he saved million times.

Background
Leo is born as one of the Twelve Demonheart Series to save humans from the attack of demons. First, he was frail and the weakest of the series. But he himself empowers thousands of demons single-handedly and became the strongest being in the whole world.