Speed-o'-Sound Sonic

Sonic is a slim young man of unremarkable height, his long black hair pulled into a topknot that lends him a faintly feminine air while bangs spill down over his face. A pair of purple marks sits beneath his large gray eyes. His usual outfit is a snug black bodysuit reinforced with metal plating over the arms, shins, shoulders, waist, and chest, trailing a long purple scarf that hangs to his legs.

His duel with Genos cost him both scarf and topknot, cropping his hair short for a stretch, though by his later appearance during Saitama and Tatsumaki's clash the flowing hair and purple scarf have both returned.

A composed exterior conceals a man who lives for combat, driven in equal measure by bloodlust toward weaklings and by the thrill of testing himself against those he cannot yet beat. His ego is enormous: once he sets his mind on a kill he will not relent until it is finished, and he cannot tolerate anyone stronger who has bested him. He prizes no life but his own and takes open pride in never leaving an opponent breathing, feeding a cynical contempt for the world and for heroes especially, whom he tells Genos can neither defeat a truly strong foe nor protect anything.

Yet a softer streak surfaces during his training to topple Saitama, when he opens up to the hunter Frank about his inner turmoil and befriends a piglet he names Ino. Rather than accept endless defeat, he trades away his humanity by devouring a monster cell handed over by Gale Wind and Hellfire Flame, though he still respects Saitama enough to vow never to strike the hero while he is fighting monsters. Much of his hatred traces to a massacre nine years earlier, when Blast descended on the Ninja Village and slaughtered his Class 5 regardless of age; only his standing as the strongest let him slip away, and the trauma reshaped his view of the world. He came to believe no one deserves the label of hero, arguing the hero industry differs little from the Village's assassination trade.

In his youth he was a spirited boy who refused to let the Village's torment grind him into a machine, dreaming of climbing to the top of its ranks so he could tear down its structure and raise orphans of similar circumstance in a freer, more open world, a dream he hoped Flash would help him reach.

Fubuki rates Sonic's combat prowess as that of an S-Class fighter, and the webcomic later confirms the ranking outright. A seasoned ninja and assassin, he wields a broad arsenal of ninja weaponry, conceals his presence, and moves at speeds the eye can barely track, beheading nearly the entire Paradisers gang in moments and slipping past every attack of the Deep Sea King. Dragon-level foes such as Gale Wind, Hellfire Flame, and Energiser have overwhelmed him, but each loss to Saitama drives him into fierce training that lifts him to where he can trade blows with Flashy Flash and hold his ground against the Heavenly Ninja Party.

Though thin, he is stronger and far tougher than an ordinary person, crediting that durability to the countless beatings Saitama once dealt him. His ninjutsu spans afterimage techniques from the Two Shadows Burial up to the ten-image Ten Shadows Burial he devised specifically to beat Saitama, alongside the Wind Blade Kick and storms of exploding and homing shuriken. His webcomic repertoire grows to include Electricity Manipulation and a Speed of Sound Electric Discharge Fist that fells armored Neo Heroes with a single poke, and with the Legendary Demon Blade gifted by Saitama he cuts down the Dragon-level machine Shunpo. He even turns a monster cell into a fancy dinner, hinting at some culinary talent.