Speed-o-sound Sonic

He is 25 years old.

He is a former member of the 44th Graduation Class of the Ninja Village, nicknamed The End (終わり, Owari; Viz: The Final).

Sonic is also a self-declared eternal rival of Saitama.

Sonic is a slim young man. 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 latex 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.

Despite his normally calm demeanor, Sonic loves fighting, as he is motivated by bloodlust against weak opponents, the thrill of battle and his superiority against strong opponents he can beat, as well as competition against a strong opponent he can't beat. Sonic has a large ego; when he sets his mind to killing someone, he refuses to give up until he succeeds and is unwilling to tolerate the existence of someone more capable who has defeated him. Sonic has no regards for human life other than his own, and even takes pride in the fact that he has never let an opponent live.[11] To that end, he holds considerable disdain for the world, being quite cynical, especially towards heroes. This is shown when he meets 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, Sonic has a soft side, as seen when he trains 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 pacing himself, Speed-o-Sound finds and befriends a little piglet as well, naming it Ino, thus showing his more noble side. When Sonic 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.

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 of 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.

In his youth, Sonic was a passionate boy who strove for a better life and did not allow the torturous training of the Ninja Village to turn him into a machine. He wanted to become the highest-ranking officer of the Ninja Village to change the institution and allow the trainees to live more freely. He expressed that the true value lies in living freely and hoped that Flash would support his dreams.

As a veteran ninja and assassin, Sonic excels in ninja weaponry, possesses remarkable speed, and is adept at hiding his presence. Fubuki comments that Sonic's combat prowess is that of an S-Class individual.[4] However, he was rather helpless against Dragon-level monsters, as seen in his fights with Gale Wind, Hellfire Flame, and Energiser. After each defeat by Saitama, Sonic dedicates himself to intense training, resulting in significant improvements in his capabilities. He now stands capable of holding his own against Flashy Flash, a powerful S-Class hero, and withstanding two of the hero's most powerful techniques. Additionally, while fighting alongside Flash, Sonic proved strong enough to eliminate all 21 members of the Heavenly Ninja Party.

Immense Speed and Reflexes: Sonic possesses superhuman speed and agility. When confronting the Paradisers, he was capable of easily moving faster than they could react, and decapitating every single member of the group apart from their leader Hammerhead, in only mere moments. He was also able to easily dodge all attacks from Deep Sea King, a Demon-level monster capable of outmaneuvering A-Class heroes with ease, only having difficulty when the sea monster entered its true form. During his fight with Genos, an S-Class hero, Sonic was capable of keeping up with the cyborg in combat, their movements being too fast for Fubuki to perceive.

Over time, Sonic underwent significant strengthening and increased speed thanks to his fights with Saitama and consistent training. This was shown when was able to keep up with Flash, a hero renowned for his exceptional speed, during a brief battle, managing to react to and defend against two of the hero's ultimate techniques.

Enhanced Strength: Despite his thin build, Sonic is stronger than the average human. He was able to dislocate Base B's shoulder and incapacitate Special Moves Mile with no apparent effort.

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.[23] During a brief fight with Flash, he was capable of enduring a lot of punches from the fellow ninja and getting back up without severe injuries.

Flashy Flash is Sonic's childhood friend. They both grew up and trained in the same ninja village, in class 5, the worst class of all. With over effort and over training. Flashy Flash wanted to kill Sonic by poisoning him before graduation, when Flashy Flash carried out a massacre against all the ninjas in the village, to exercise justice and eliminate them.

Sonic survived the poison and became an S-class criminal.

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