Speed-o'-Sound Sonic/Other Media

Prison
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," Puri-puri Prisoner, to shout at the other prisoners in irritation. After listening to a description of Puri-puri Prisoner, Sonic then witnesses his breakout due to watching the Deep Sea King's rampage on television; recognizing his strength, he follows the man out of the prison.

Sense
Sonic encounters Saitama in the K-City Nature Park and challenges him to a fight once more. He tries out his new equipment against Saitama and initially it seemed to work. However once again, Sonic loses when Saitama accidentally elbowed him in the groin and he lets Sonic go again.

Confidence
Following on from Speed-o'-Sound Sonic's decision to eat a Monster Cell, Sonic has diarrhea for the whole night. After the ordeal, Sonic believes he has become a monster and that while, he hasn't changed his appearance, his body has undergone a massive change. He has vindictive thoughts about Gale Wind and Hellfire Flame for not telling Sonic about the diarrhea. However he puts the thought aside as he never planned to join the Monster Association, he feels great power within himself. Feeling lighter and more powerful, Sonic is brimming with confidence and states he will need time to adjust to his new body. In reality, Sonic just lost 2 kg from his diarrhea and is mistaking his condition as his new monster form.

The Ninja Who is Too Complicated
After losing against Saitama, Sonic began having nightmares and flashbacks of the incident. His confides his worries to a matagi, who consoles him about his fears. As he was training, he saved a small baby boar, who he later named Ino and together began training to become stronger. He regains his confident and after defeating Saitama in his visual training, he decided to leave, saying farewell to the matagi, who later corrected him about his name. Sonic later silently watched over the city, ready for his next battle.

Sonic, Becoming Saitama
Sonic challenges Saitama to another match and Sonic experiences his 11th loss. Frustrated over his lack of progress against Saitama, Sonic decides to experience life as Saitama in order to uncover his weakness. Sonic disguises himself as Saitama, imitating his looks and speech patterns. Genos comes across Sonic and mistakes him for Saitama. Sonic lies about encountering a monster that hit his head, making his memory foggy and forgetting Genos' name. Genos is shocked and asks where the monster is to which Sonic replies it ran away into the mountains. Genos leaves to give chase to the monster and kill it.

To understand Saitama further, Sonic heads towards the Hero Associaiton. There, he encounters Kamikaze. Kamikaze questions why Sonic is there and is annoyed at Sonic's attitude. Sonic draws his blade but Kamikaze blocked it with his sword with such speed that Sonic didn't even see the blade being drawn. Tatsumaki enters the room and berates Sonic as she is annoyed that a weak B-Class was summoned for the mission. Sonic, not understanding who Tatsumaki is, believes that she used her cuteness to make it into S-Class. Tatsumaki demands Sonic leave which he does with his smokescreen shuriken leaving her and Kamikaze coughing.

Sonic, angry over his experiences so far, wonders that perhaps Saitama is suffering horrible treatment he receives from the public. A monster called Angry Grandpa kidnaps a child. Mumen Rider arrives a delivers a Justice Tackle to free the child and a Justice Punch and Justice  Kick followed by a Justice Crane High Kick. Sonic saves Mumen Rider from a powerful attack and they finish off the monster. Mumen Rider thanks Sonic for his help and Sonic asks why he is a hero since he almost died. The child gratefully thanks Mumen Rider and Sonic for saving him. Mumen Rider decides to contact the Hero Association to collect the monster. Mumen Rider leaves, suggesting they go drinking sometime.

Sonic understands why Saitama decided to become a hero but not his strength. As Saitama battles monsters on a daily basis, Sonic decides to see if he can uncover the secret of his strength in battle. Sonic comes across Energiser who he recognized from the secret documents he stole from the Hero Association. He informs Energiser that Tornado of Terror and Atomic Samurai are hunting him and that he plans to take him down by himself. They engage in battle. Despite his skill, Sonic loses the battle and almost dies if it weren't for the timely arrival of Saitama.

Together they take down Energiser. Saitama's questions Sonic' attire and asks if he wants to be a hero. Sonic says he's not and that he knows Saitama's weakness. Once more, Sonic declares that he will end Saitama's life. Sonic then leaves with a final message saying that Saitama will soon know his weakness. Sonic decide that he had enough playing hero and that as long as he is fighting monsters, Sonic won't attack Saitama. He once again decide that the only way to beat Saitama is to hone his skills further.

Junior high school student Saitama Episode 3
Sonic to transfer to Z Municipal Peace Middle School to settle a dispute with Saitama. Currently, there is a sports festival. Sonic, who wanted to beat Saitama, has become on the same team as him and struggles to win.