Speed-o'-Sound Sonic

Speed-o'-Sound Sonic is a villain in the series, first appearing as a bodyguard hired by Mr. Monier. He occasionally takes the role of an anti-hero. He views Saitama as his eternal rival. Sonic is a thin man who, despite his slender build, is extremely strong and fast. He has a feminine face, black medium length hair that is tied up in a topknot, and large, light brown eyes. One noticeable feature is that he has two purple marks under his eyes, one under each. He also has multiple scars on his chest and his arms. He first appears wearing a tight black outfit highlighted by metal plating on the shins, fore-arms, shoulders and chest, as well as a long red scarf. He is shown later in black street clothes. He always carries a ninjato and other ninja equipment such as kunai and shuriken.

Despite his normally calm appearance, 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 Hammerhead's gang and even goes as far as to take pride in the fact that he never lets a single person live. He also seems to be rather disdainful of heroes. When he meets Genos, he tells him that heroes can neither win against a truly strong opponent nor can they truly protect anything. However, unlike Garou, he does not go out of his way to attack heroes. Sonic first appears as a bodyguard for a character named Mr. Monier, defending him from a group calling themselves the Paradise Group. Sonic appears before the group and their leader, Hammerhead, as they are approaching Monier's building. After appearing before the group and claiming that he has never let a single person live he quickly dispatches all of the group except the leader who is able to block Sonic's attack in time. After avoiding and subsequently mocking Hammerheads attacks, Sonic hits him in the back of the head with a kunai. Assuming that Hammerhead has been defeated, he calls in to report his success but when he turns back he sees that Hammerhead is gone. Following after him he meets Saitama whom he then attempts to attack, first with a kunai that Saitama catches, then with his sword - which was also caught and subsequently broken by Saitama. Saitama tries to explain that he isn't part of The Paradise Group and that he's actually a hero who has saved the world several times, but Sonic doesn't listen and says that his pride won't let him have had someone block him that many times, Saitama then calls him out on the fact that he really just wants to fight him because Saitama is strong. A fight ensues that shows off Sonic's incredible speed, only to end abruptly when the ninja runs his crotch into Saitama's fist. Sonic quickly leaves, claiming that because he has found a strong opponent he was leaving to train, claiming that the next time they meet would be the last and that he would kill Saitama. All the while withering in pain from injuring his groin. Saitama is running about, worrying about losing his heroes license when Sonic throws a kunai at him and he catches it. Sonic begins to threaten Saitama, but Saitama interrupts him, saying that they could do this another time and begins to walk away. This angers Sonic who then draws his sword and rushes at Saitama to attack, but Saitama quickly turns around and bites Sonic's sword in half. Sonic stands still for a second, confused by what had just happened until Saitama threatens to punch him, causing Sonic to shudder from the menacing aura. At that point the two of them are distracted by Tanktop Tiger who has shown up to investigate the person who'd been running around town (Saitama) and starts to threaten Saitama until Sonic throws several exploding shuriken at him which cause him to pass out. Observing that Saitama is a hero, Sonic declares that he will create a situation that will force Saitama to fight him, then jumps back and throws several more exploding shuriken which Saitama is prepared to block, but instead fly off in several directions, hitting the surrounding buildings and causing a lot of mayhem. Sonic continues to do this until Saitama jumps up behind him and karate chops him in the back of the head which throws him to the ground hard enough that it leaves an impression of his gleeful face in the pavement.

As Sonic became a villain, he is quickly taken to prison, but manages to break out several times, often in the blink of an eye, until the guards are forced to put him in restraints and send him to the maximum security Smelly Lid Prison. There, he effortlessly defeats the prisoners who dare to challenge him, even causing one to scream out in pain, which in turn causes the "boss", Pri-Pri Prisoner, to shout at the other prisoners in irritation. After listening to a description of Pri-Pri Prisoner, Sonic then witnesses his breakout due to witnessing Sea King's rampage, and, recognizing his strength, follows him out of the prison. Sonic escapes from prison when Pri-Pri-Prisoner broke out to save J-City from the Sea King. Sonic watches the fight between Pri-Pri and Sea King and notices that Pri-Pri was acting tough and he is really in trouble and that he can take out both of them with no problem. After Sea King defeats Pri-Pri, Sea King annoyed Sonic which made him want to fight him. Sea King attempts to punch Sonic who easily dodges causing Sea King to attack Sonic several more times, with Sonic dodging the attacks and eventually landing a kick on Sea Kings face. After landing the kick a snake-like thing appears in front of Sonic and attempts to bite him, but only manages to rip his shirt. The snake-like thing is actually a long Moray that is coming out of Sea Kings mouth. Sea King goes to attack with his Moray again, but Sonic dodges it and smashes Sea King's mouth shut, causing him to bit off the Moray. Sea King then attempts to use a chain punch on Sonic, who easily dodges and jumps at Sea King, attacks him and lands on the roof of a nearby building, but when he looks back, Sea King is laughing. Sea King the launches himself at Sonic and crashes into the roof of the building, with Sonic barely being able to dodge in time. After dodging away from Sea Kings attack, Sonic jumps off to a different building, but before he has a chance to do anything, Sea King shows up. Sea King then reveals that after he'd left the sea his body had shriveled up, but the rain he enabled him to return to his true form. Sonic runs away, leaving behind his prison outfit in the Sea King's grip. Sonic then appears on a nearby roof naked, vowing that the next time the two would meet would be their last, after which he leaves. Then he meets Genos on the way who asked him who he was. Instead, he warned him about the Sea King and leaves. Sonic returns with his full ninja outfit, prepared to fight the Sea King once more, but is too late, as Saitama had already eliminated the Sea King. His persistence to beat Saitama continues and went to his place to challenge him once more. However, he ended up facing Genos who introduced himself as Saitama's disciple. They begin their battle and are on equal footing. Genos can't catch up with his speed but his attacks aren't hurting Genos either. Genos attacks him again but evaded. The impact caught Miss Blizzard, who was fighting Saitama at that time. However, Saitama quickly got between Blizzard and the explosion. Sonic retaliates with exploding shurikens, but is still unable to hurt Genos. Saitama stops the two of them from fighting each other. Saitama then accepts Sonic's invitation to a fight. Sonic reveals his newly learned technique, but still questioning whether he can beat Saitama. Saitama then uses one of his "Serious Series" moves to beat Sonic. Sonic once again promises that he will defeat Saitama the next time they meet and then vanishes.