Speed-o'-Sound Sonic, birth name unconfirmed, emerged from the Ninja Village's 44th Graduation Class under the moniker "The End." He deliberately endured Class 5—the lowest rank—to maximize his training's harshness. During his youth, he forged a bond with Flashy Flash, sharing ambitions to dismantle the village's oppression. This worldview shattered after two traumas: Flashy Flash poisoned their class (Sonic survived via resilient constitution), and Blast later massacred the village, leaving Sonic as the sole survivor. These events cemented his cynicism toward heroes, whom he deemed hypocrites cloaking violence as justice. Sonic possesses a slender, androgynous frame with gray eyes and distinctive purple markings beneath them. His long black hair was originally tied in a topknot until Genos severed it mid-battle; though it regrew, he retains shorter hair. He dons a black latex bodysuit accented by metal plating on his shins, arms, shoulders, chest, and waist, always paired with his signature purple scarf. Beneath a calm exterior lies ferocious bloodlust in combat. Sonic relishes challenging powerful foes and obsessively pursues those who defeat him—particularly Saitama, declared his eternal rival after an embarrassing first encounter. Arrogant and intolerant of superiors, he claims no regard for human life and takes pride in never sparing opponents. Paradoxically, he exhibits sporadic compassion, such as befriending bear hunter Frank or adopting a piglet named Ino during training. His disdain for hero organizations stems from viewing them as corrupt, ineffectual entities indistinguishable from assassins. His prowess blends ninjutsu mastery with superhuman physicality, rated S-Class by Fubuki. Core abilities include Immense Speed and Reflexes—enabling supersonic movement, effortless evasion, and slowed-time perception—plus Enhanced Strength (dislocating limbs effortlessly) and Enhanced Durability (withstanding impacts like Deep Sea King's strikes). Techniques span shadow illusions (Four/Ten/Thirteen Shadows Burial), explosive projectiles (Hail of Carnage), and specialized strikes (Wind Blade Kick, Speed of Sound Electric Discharge Fist). Standard armaments include a Ninjato, kunai, Exploding Shuriken, and Smokescreen Shuriken. Sonic evolves across his exploits. Initially Zeniru's bodyguard, he encountered Saitama while pursuing Hammerhead. After repeated humiliating defeats by Saitama—including arrest post-city rampage—he committed to grueling training. He briefly allied with Puri-Puri Prisoner during a prison break and retreated from Deep Sea King post-transformation, later warning Genos about the threat despite their rivalry. His fixation on Saitama drove techniques like Ten Shadows Burial. He nearly consumed a Monster Cell for power but suffered severe diarrhea after cooking it, voiding its effects. Recently, he confronted the Heavenly Ninja Party alongside Flashy Flash and battled Neo Heroes operatives, demonstrating heightened speed and tactical synergy. Key relationships shape his path: an obsession with Saitama fuels most actions, though he avoids interfering in Saitama's monster fights. His history with Flashy Flash intertwines rivalry, respect, and unresolved tension from their shared past. Antagonism toward Genos and heroes like Tatsumaki underscores his ideological rejection of organized heroism.