Spinthir attacks Calvaria, a defence nation, since they are on the same piece of land. With Yūgo and Yūma Kuga's support, things went in favour of Calvaria. However, one day, Yūma disobeyed Yūgo's orders to not fight and went out in battle, where he was severely injured by an unknown party. On the brink of death, Yūma was saved by his father, who sacrificed himself by turning himself into a Black Trigger and replaced Yūma's real body with a Trion Body. After 3 more years of war, the war ended, with Yūma's victory. Since the war ended, Yūma decided to go to Mikado City to find a way to revive his father and restore his body, as well as meet his father's acquaintance.