Sonic is one of the reoccuring villains in One Punch Man and is Saitama's self-proclaimed "rival"

Speed of Sound Sonic is a ninja. Except, without being a ninja.... He has an arsenal of high-tech shirukens, throwing knives, and his sword in fights. He uses hiis high speed and martial arts to fight his oponents.

Despite looking pretty calm, Sonic loves fighting strong opponents . He has this "bad habit" when fighting and pretty much can go crazy at any time. He is persistent, even when he knows that his opponent is stronger than him. Sonic does whatever he can to start fights, like causing massive property damage, endangering the surrounding citizens, and being an overall loon in order to get Saitama to fight him. Plus,he becomes more of Genos' rival than Saitama. 

A high voice for him. Think of TeamFourStar's Frieza. the voice should sound calm and confident, while also sounding a bit sinister.