Nabuca (ナブカ) is both a rival character for Shu and an important character for the plot.
Nabuca is intelligent, mature, and always one step ahead of his opponents, making him the top kid in the military. He fights in the military to survive, hoping one day he will go back to his village. He is very merciless, he will kill anyone and everyone in order to achieve his goals. He hates people thinking that he owes them a favor.
Nabuca is very strong and has critical thinking. He has dark hair and eyes with a stern and strong voice. His main weapon of choice is the rifle, and his off-hand is the knife.
Nabuca is first shown in episode 1 chasing Shu. After a while Nabuca and Shu get in a fight. At the beginning of the fight they both knock each other's weapon out of their hands and end up trading weapons. While fighting Shu knocks Nabuca off him, and into the railing, subsequently destroying the railing. Nabuca falls, but grabs onto the broken railing. It shows how the railing cannot support his weight, and he is about to fall into a furnace. Shu then grabs onto the rail attempting to help Nabuca up, eventually the railing falls and Nabuca grabs Shu's hand. A short minuite after resting Shu gets knocked out by another person.