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.

Introduction Arc
Yūma is first seen after getting involved in a car accident. Despite being hit by a car, he is unscathed. The owner and a police officer ask if he's alright, but he just apologizes, saying it's his fault, and even offers to repay for the damage in the car, which the owner rejects. The police officer then asks Yūma's address and Replica dictates it for Yūma to repeat. Hurrying to his school as Replica says he's late, Yūma asks if he can use his Trigger. Replica says it's Yūma's decision, and Yūma decides not to use it. Getting in his school, Yūma looks inside a classroom (in the anime, Chika's classroom) and notices all students dress up similarly, and questions if it is trendy, and Replica says it's actually a way to identify the institution, which causes Yūma to compare the school to a military institution.

Yūma is then spotted by a teacher, and is taken to the right class, accompanied by teachers Moribayashi and Mizunuma. There, he introduces himself. A student then points out that Yūma has a ring, and Moribayashi orders Yūma to hand it over, but Yūma refuses to. Mizunuma then explains to Yūma that students aren't allowed to wear accessories and Yūma apologizes for interrupting the class, trying to leave. The teachers try to convince Yūma to stay, and Osamu, who was quiet all along, says Yūma might have a reason for not wanting to give away the ring. When questioned about that, Yūma says it's a memento from his dead parents, and

Introduction Arc

 * Yūma Kuga vs. Miwa Unit: Win

Border Enlistment Arc

 * Yūma Kuga vs. Shun Midorikawa: Win (8-2)

Large-Scale Invasion Arc

 * Yūma Kuga vs. Viza: Win

B-Class Rank Battles Arc

 * Mikumo Unit vs. Yoshizato Unit vs. Mamiya Unit: Win
 * Mikumo Unit vs. Suwa Unit vs. Arafune Unit: Win
 * Mikumo Unit vs. Nasu Unit vs. Kuruma Unit: Win
 * Mikumo Unit vs. Ninomiya Unit vs. Azuma Unit vs. Kageura Unit: Loss (Ninomiya Unit's victory)