9ine is a red-skinned man with white hair styled in a coqui, appearing elderly despite being around thirty years old. He typically wears a white coat, torn pants, and a distinctive 9-shaped gold earring on his left ear. His katana, carried on his back, has a gourd tied to its sheath; he also carries kunai throwing knives and a lighter.

Once a member of the Red Ronin, a band of forty-seven samurai, 9ine served as a ruthless mercenary. After a critical mission failure, he abandoned the group and became a nomadic, often drunken, wandering swordsman. He sporadically clashes with former comrades like 12welve, with whom he shares unresolved history.

9ine possesses superhuman speed, agility, and strength. He is an acrobatic master of hand-to-hand combat and swordsmanship, capable of slicing through bullets and swiftly disabling multiple foes. His physical abilities surge dramatically when intoxicated. He uses his lighter to ignite alcohol fumes exhaled from his mouth, unleashing waves of blue flame.

He encounters the main group early in their journey. Following initial hostilities, he forms a temporary alliance, departing after two episodes. He later reappears during a pivotal battle against the Red Horizon Foundation, intervening decisively to aid the protagonists. When not fighting, he exhibits a detached and lethargic demeanor, frequently lazing or drinking.