Speed-o'-Sound Sonic originated in the Ninja Village, enduring its severe training from birth. As part of the 44th Graduation Class, known as "The End," he deliberately hid his potential, ranking last in the lowest tier, Class 5, to subject himself to harsher drills for greater growth. During this time, he forged a connection with Flashy Flash, both aspiring to reform the village's oppressive structure and grant trainees more liberty. Nine years before the main events, Blast assaulted the village, slaughtering all Class 5 ninjas. Sonic alone escaped due to his strength, an experience that cemented his cynical outlook and intense disdain for heroes, whom he perceives as hypocritical figures no better than assassins. Physically, Sonic presents as a slim male of average height. He possesses long black hair, typically secured in a topknot, and gray eyes highlighted by distinctive purple facial markings. His standard outfit is a black latex bodysuit featuring metallic plating on the shins, arms, shoulders, and chest, always paired with his signature long purple scarf. While imprisoned, he wore a standard prisoner uniform. After Genos severed his topknot in combat, his hair appeared shorter temporarily, though he later restored his original appearance, including the scarf. Sonic's personality is marked by arrogance, bloodlust, and a fixation on surpassing powerful foes, relishing combat and declaring defeated opponents like Saitama "eternal rivals." His hatred of heroes stems directly from Blast's attack, leading him to dismiss their justice as mere pretense. Despite professing ruthlessness—claiming he "never lets opponents live"—he displays unexpected compassion, befriending a hunter named Frank during training and adopting a boar named Ino. He also warned Genos about the Deep Sea King, revealing a nuanced moral code. His obsession with defeating Saitama drove him to consume a Monster Cell; cooking it negated the effects, resulting only in severe diarrhea and weight loss. His primary abilities center on ninjutsu mastery and superhuman speed, earning Fubuki's assessment as S-Class caliber. His physical prowess includes enhanced strength, dislocating shoulders effortlessly, and notable durability, withstanding strikes from S-Class opponents—attributes he credits to surviving Saitama's punches. Techniques emphasize speed and deception: the Full Frontal Attack, Wind Blade Kick, and Shadow Burial variants (Two, Four, Ten, and Thirteen) create afterimages to confound enemies. His Exploding Shuriken Ferocious Barrage homes in on targets, while the Speed of Sound Electric Discharge Fist delivers lethal shocks. Innovations like imitating Saitama's Serious Side Hops often exhaust him with limited effect. His equipment includes kunai, exploding shuriken, and the Legendary Demon Blade gifted by Saitama, which he wields against Dragon-level threats. Sonic's development spans multiple storylines. Initially Zeniru's bodyguard, he slaughtered the Paradisers before clashing with Saitama, who defeated him via an accidental groin punch. This humiliation ignited his rivalry, leading to repeated failed challenges and a prison stint after causing citywide chaos. During the Sea Monster arc, he escaped prison, fought the Deep Sea King unarmed, and retreated upon recognizing the monster's rain-enhanced power. Later, he confronted Genos as Saitama's "disciple," demonstrating equal combat skill until Saitama intervened. In the Monster Association arc, he rejected Gale Wind and Hellfire Flame's offer to join their ranks but consumed their Monster Cell for power, resulting in comedic failure. During the Neo Heroes saga, he allied with Flashy Flash against the Heavenly Ninja Party and later eliminated Neo Heroes agents using his electric techniques. Spin-offs and OVAs further explore his persistence and softer aspects. In "The Ninja Who is Too Complicated," he bonded with Ino while training and regained confidence post-defeat. "Zombieman Murder Case 2" depicted him freezing during a mountain ambush attempt on Saitama. Audio dramas revealed his impersonation of Saitama for study, temporarily aiding Mumen Rider against a monster before reaffirming his non-heroic stance. He also declined Puri-Puri Prisoner's offer to return to prison, asserting his independence.