Killer, a pirate originating from the South Blue, serves as the primary combatant for the Kid Pirates under Captain Eustass Kid. His bond with Kid traces back to their childhood, forged by a shared crush on a girl who rejected them both after an incident involving spilled curry udon. This early connection solidified into a lasting partnership, leading them to found their pirate crew together. Killer possesses a tall, muscular build and is almost always concealed behind his signature full-head helmet mask. Post-timeskip depictions show him with a goatee, longer blonde hair, and a blue shirt featuring the crew's Jolly Roger. Known as the "Massacre Soldier," Killer holds a bounty of 200,000,000 berries after the timeskip, marking him as one of the eleven Supernovas and a member of the "Worst Generation." His combat style emphasizes agility and speed, utilizing specialized wrist-mounted rotating scythes called Punishers for swift strikes and defensive maneuvers, often combined with kicks. He demonstrates proficiency in both Observation and Armament Haki. A significant shift occurred when Killer consumed a defective SMILE Devil Fruit in Wano Country, stripping him of the ability to express any emotion except forced laughter ("Faffaffaffa"), a condition he despises. To protect Kid from the Beasts Pirates, he adopted the alias "Kamazo the Manslayer," working as an assassin for shogun Kurozumi Orochi. During this period, he abandoned his mask, wore bandages and a sickle-patterned kimono, and embraced ruthless violence, though he spared non-targets who yielded. After failing an assassination and reuniting with his crew, he resumed wearing his damaged mask. In *One Piece: Stampede*, Killer participates in the Pirates Festival on Delta Island alongside Kid and rivals. During the battle against the former Roger pirate Douglas Bullet, he demonstrates loyalty and coordination with Kid, rescuing his captain when Bullet destroys the floating treasure island and they fall into the bay. He later joins the collective effort of the Worst Generation to confront Bullet, though their combined assaults prove ineffective against Bullet's strength and Devil Fruit powers. During the fight, Killer employs his battle cry "FAFA" while attacking, and his blades fail to pierce Bullet's Armament Haki. He persists in supporting Kid throughout the chaos. Killer's personality balances Kid's impulsiveness with pragmatism, frequently advising caution or diplomacy, such as when mediating tensions between Kid and Scratchmen Apoo. His loyalty to Kid is absolute, driving him to accept Orochi's SMILE terms to save his captain. This devotion extends to his crew, who reciprocate by adopting his forced laughter out of solidarity. Though confined to expressions of joy by the defective SMILE, he remains a strategically focused combatant in high-stakes conflicts.