Yūma Kuga/Plot

Background
When he was 6, Yūma's father Yūgo Kuga taught him "The Three Teachings".

When Yūma still lived in the Neighbor world, he and his father, Yūgo, participated in the Civil War between Calvaria and Spinthir, helping Calvaria as a favor to a friend of his father. One day, Yūgo told Yūma not to participate in the battle because earlier that day they had found the dead bodies of some of their men, and they were some of the most powerful of their side. Yūma's father suspected it was the result of the other side having a Black Trigger, so he wanted to keep Yūma out of danger. Yūma, however, just pouted and didn't really think much of his father's words.

After his father had left to go fight, Yūma left Calvaria's fortress and went to the battlefield. Seeing multiple battles he could help win, he decided to make attacks behind the scenes and eliminate some of the enemy units. But before he could do that, he was approached by a mysterious enemy, and wasn't strong enough to defend himself, resulting in his death. As Yūma laid there dying, his father came to his aid, and took out his own black trigger. He then sealed the body of the dying Yūma inside the trigger, substituting it with a body made of Trion (which is the reason his hair is white); thus saving Yūma. Unfortunatly, this took all of Yūgo's power. And so he turned to dust, crumbled and died. However, this does not mean Yūma is immortal; Yūma's real body is sealed inside his ring and is slowly degrading. And once his body inside his ring is fully gone, it is most likely Yūma's Trion body will also be terminated.