Speed-o'-Sound Sonic (音速のソニック, Onsoku no Sonikku), more commonly called Sonic, is a recurring villain and occasional anti-hero. He first appeared as a bodyguard hired by Zeniru. He is a former member of the 44th Graduation Class of the Ninja Village, nicknamed "The End". Sonic is one of the few people aware of Saitama's true strength and is a self-declared eternal rival of Saitama.
Sonic is a slim young man with an androgynous appearance. His long black hair is normally tied up in a topknot, and bangs fall over his face. A noticeable feature of his is the purple marks underneath his large gray eyes. He usually wears a tight black bodysuit highlighted by metal plating on his shins, arms, shoulders, chest, and waist, as well as a long purple scarf that falls to his legs. During his fight with Genos, Genos ripped his scarf and tore off his topknot, leaving the ninja with short hair.
Despite his normally calm demeanor, Sonic loves fighting strong opponents as shown by when he gets a "child-like smile" on his face when he first meets Saitama and has two of his attacks blocked, earlier calling this his "bad habit." He seems to be very quick to act as he attacks Saitama on their first meeting without letting him explain the situation.
He is persistent, even when he realizes that the opponent is much stronger than he is. When Sonic recognizes an opponent as his rival, he does whatever he can to initiate the battle, such as causing massive property damage and endangering the surrounding citizens in order to get Saitama to fight him. He also seems to have no qualms with killing as shown when he kills the Paradisers and even goes as far as to take pride in the fact that he never lets a single person live, although it is currently unknown if he has killed innocent lives or has no problem with killing civilians.
He used to be kinder and more sociable growing up, only wishing to give his fellow orphans more freedom in life. But the showy display of power and ruthlessness portrayed by the hero Blast and his employers in the Hero Association jaded him considerably.
To that end he holds considerable disdain for the world, especially towards heroes. As shown when meeting Genos for the first time, he tells him that heroes can neither win against a truly strong opponent nor can they truly protect anything.
Despite the way he presents himself, he seems to actually retain his softer side. Something which is seen when he is training to fight against Saitama. During this period, he spent a great deal of time with Frank, a hunter who had almost been killed by a bear and confides with him his inner turmoil. While he is training, he finds and befriends a little piglet as well, naming it Ino, thus showing his more noble side. When he leaves to search for Saitama, he gives his words of wisdom to Frank, saying that if he is too confident in his fighting style and loses, the result will always be the same. It is unclear as to how far this side of him goes to, as he was willing to warn Genos of the Deep Sea King, yet fought him when Genos interfered with his battle with Saitama.
Due to constantly losing to Saitama, Sonic is shown willing to do anything, even trading his own humanity, to defeat him by becoming a monster through the consumption of a Monster Cell provided by Gale Wind and Hellfire Flame, although he feels that becoming a monster is equal to dying, since he will be no longer human. At the same time, he is also shown to have some class as he cooks the Monster Cell properly before consumption since he cannot stand raw food.
Part of the reason why Sonic despises the hero industry is due to hating how similar it is to the Ninja Village's practice of breeding and selling brutal murderers on the black market. This coupled with hating how powerful people with an inflated sense of self-worth often bandy their greater ability for superficial purposes perturbs his ire towards them considerably.
Despite this however, Sonic also respects Saitama for fighting monsters and even promised to himself to never fight Saitama while the hero is fighting monsters. He holds a very negative view towards the Hero Association and some S-class heroes after observing how they treat a powerful hero like Saitama like a low-ranked and worthless hero because of his looks. Ironically, he is also rather judgmental as he assumes Tatsumaki exploits her childish cuteness and that those with benign appearances are weaker than himself, displayed in his fight against Saitama and Kamikaze.
Abilities and Powers
As a ninja, Sonic is adept at hiding his presence. He has displayed proficiency with multiple weapons. Fubuki commented that Sonic's fighting ability is that of an S-Class individual. It was also mentioned by Gale Wind that Sonic and Flashy Flash are the sole survivors of the 44th graduation class, "The End", from their village. However, he is rather helpless against Dragon-level monsters, as seen in his fights with Gale Wind, Hellfire Flame, and Energiser.
As a child, he was revealed to have been rather weak in comparison to other ninjas, as he was always placed in the lowest class and was unable to advance to higher classes despite being given the harshest training in Class 5. However, Sonic revealed that like Flashy Flash, he only acted like he was weak in order to receive the harshest training.
After his self-training, he appears to have found a more effective way to increase his power, and was able to fight on-par with Flashy Flash, surprising the hero. What's even more astounding is that he was able to withstand one of Flashy Flash's ultimate moves: Flashy Kick. Additionally, while fighting alongside Flashy Flash, Sonic was strong enough to eliminate all 21 members of the Heavenly Ninja Party.
Immense Speed and Reflexes: Sonic's main power lies in his immense speed. Sonic was able to easily dodge rocks thrown by Hammerhead and dodge the Deep Sea King's attacks. Sonic is faster than the S-Class heroes Genos and Metal Bat.
He could easily keep up with Genos and was able to catch up with Tatsumaki. Additionally, he appears to have become significantly stronger and faster due to his fights with Saitama, as he was able to surprise Flashy Flash several times during their sparring match.
Enhanced Durability: Sonic's durability is greater than the average human's. He withstood Base B's shoulder and dislocated the prisoner's shoulder in turn.
During his fight with Flashy Flash, his durability was shown to have significantly increased, and he was able to withstand Flashy Flash's Flashy Kick.
He also withstood Brawny Muscle's special punch, who can be considered the Heavenly Ninja Party's physically strongest member. He credited this durability to having experienced Saitama's attacks over a dozen times.
Ninjutsu Master: Sonic is a master of ninjutsu and has knowledge of various deadly techniques.
- Full Frontal Attack (正面からまっすぐに狩る, Shōmen kara massugu ni karu): Sonic takes a low stance and rushes forward at speeds that make him impossible to be seen. The effect of this attack is not known because it was interrupted by Hammerhead.
- Wind Blade Kick (風刃脚, Fūjinkyaku): Sonic flips forward multiple times extremely quickly and uses his momentum to deliver a kick to his opponent.
- Hail of Carnage (殺戮乱陣, Satsuriku Ran-jin): Sonic throws a hail of exploding shuriken, causing destruction to his surroundings.
Expand the following section to see Original Webcomic information. Beware of spoilers.
- Two Shadows Burial (二影葬, Niei-sō): Sonic creates two afterimages.
- Sonic Heavy Barrage (音速重連拳, Onsoku Jūren Ken): Sonic delivers multiple punches to his opponent.
- Four Shadows Burial (四影葬, Shiei-sō): Sonic creates four afterimages using a special movement technique.
- Scattered Flash Slash (散閃斬, Sansenzan): Used in a conjunction with Four Shadows Burial; Sonic attacks his opponent with his four afterimages. This was used against Genos. However, the effectiveness of the attack is unknown, as Saitama saved Genos before Sonic could hit him.
- Ten Shadows Burial (十影葬, Jūei-sō): Sonic creates ten afterimages. When using this technique, Sonic reaches massively hypersonic speeds.
Serious Side Hops: (マジ反復横とび, Maji Hanpukuyokotobi) Sonic can perform an inferior imitation of Saitama's Serious Series: Serious Side Hops. Sonic hops from side-to-side rapidly. Doing so creates a multitude of afterimages in the form of a wall. Sonic then charges at his opponent, however the resulting shock wave was not strong enough to down any members of the Heavenly Ninja Party and left Sonic exhausted.
Ninja Weaponry: Sonic uses a variety of ninja-based weaponry in combat.
- Ninjatō: Sonic's primary weapon. The sword has a straight blade and a hilt and is sheathed in a black scabbard. It is extremely sharp and capable of cutting through bone.
- Kunai: Sonic carries a number of kunai and is exceptionally skilled in their usage.
- Exploding Shuriken (爆裂手裏剣, Bakuretsu shuriken): Shuriken that explode upon impact.
- Mizugumo (水蜘蛛): Literally translated to "Water Spider", wooden sandals used to walk on water.
- Homing Exploding Shuriken (ホーミング 爆裂手裏剣, Hōmingu Bakuretsu Shuriken): Shuriken that explode upon impact and home onto a target.
- Exploding Shuriken Ferocious Barrage (爆裂手裏剣 猛襲陣, Bakuretsu Shuriken Mōshū-jin): Sonic carries with him shuriken that explode upon impact and home onto a target.
- Katana: Saitama steals two katanas from the Ninja Village Leader called the Legendary Demon Swords (伝説妖刀, Densetsu Yōtō) and gives Speed-o'-Sound Sonic and Flashy Flash.
- Smokescreen Shuriken (煙幕手裏剣, Enmaku shuriken): Shuriken that leave a trail of smoke. Sonic uses them to conceal his position.
- (To Frank) "If you are too confident in your fighting style but lose... the result will always be the same."
- (Referring to Saitama) "Whenever I face you, I cannot picture myself winning for some reason... Unless I defeat you and wipe off this thought I cannot move on."
- Sonic is ranked 3rd in the character popularity poll.
- Sonic's prisoner number was 4188.
- ONE has said that Sonic with a weapon would have defeated the Deep Sea King pre-rain form.
- ONE stated a fight between him and Genos would end in a draw.
- As proof of this statement, when Genos and Sonic fight it ends in a draw, although technically Saitama intervened in this battle, preventing it from being settled.
- Sonic buys his weapons from a weapon shop.
- Sonic's black lines under his eyes are a reference to an American football player and are inspired by Eyeshield 21, another manga by Yusuke Murata.
- Murata revealed during a stream that Sonic and Flashy Flash are "somewhat" related. Chapters 78 and 95 later confirmed this directly, revealing that the two were from the Ninja Village's 44th graduation class, "The End." 
- Further information in webcomic chapters 114-116 reveal that during their class graduation, Flashy Flash killed all the other members of his class, but Sonic was sick and spared from death by Flash as both of them were friends.
|S-Class||Garou • Speed-o'-Sound Sonic|
|A-Class||Big Iron • Bull-Bull • Serial Bomber|
|C-Class||Banero • Don Pacino • Pacino Family|
|Ex-Villains||Dr. Genus • Hammerhead • Men's Esthetician Man|
|Undetermined Class||Aburabozu • Base B • Burigura • Chimagusa • Coalition of Assassins • Cow's Stomach • Demolition John • Devil Storm • Fukegao • Harold • Paradisers • Smelly Lid Old Man • Special Moves Mile|