Speed-o'-Sound Sonic vs. Deep Sea King

Speed-o'-Sound Sonic vs. Deep Sea King was the battle between the ninja assassin Speed-o'-Sound Sonic and the Deep Sea King, a Demon-level monster.

Prelude
After Puri-Puri Prisoner's fall against the Deep Sea King, Sonic asks him who he is. The monster calls himself the Deep Sea King, lord of the Clan of the Seafolk, and claims that the surface world is his to rule. Deep Sea King asks Sonic if would dare defy him, and Sonic mocks his strength and ambition, calling him pathetic. Deep Sea King now states that the ninja must die, and Sonic replies by saying that's his line.

Battle
The Deep Sea King lunges forward and strikes Sonic with a right punch, but Sonic jumps up and dodges it, countering with his Wind Blade Kick. Sonic proclaims that he sees through all of the monster's moves, but he is quickly proven wrong. A monstrous moray comes out of Deep Sea King's mouth and manages to rip part of Sonic's prison garb off. The monster asserts that once his moray latches onto something, it never lets go. The moray attempts to strike Sonic again, but the ninja rushes forward and clamps Deep Sea King's mouth shut, dismembering the moray from his mouth. With a devious smile, Sonic says that he would never lose to someone like him, and in anger, the monster attempts to grab Sonic with both of his hands, but is unsuccessful. He follows up with a string of punches which Sonic manages to easily dodge. The ninja mocks the monster by saying he focuses too much on power and lacks speed. The ninja smiles, for he realizes that fighting someone like Deep Sea King proves how strong he's become. Sonic then counters with his own barrage of attacks and jumps up a building. Then, Sonic's eyes widen when Deep Sea King attempts to punch him at faster speeds then before. Sonic narrowly dodges the attack, noting this increased speed and well as some increased strength. The monster appears behind the ninja, and Sonic shockingly realizes his huge bulking form. Sea King explains that the dry environment weakened him, but with the coming rain, he transformed to his true form, also proclaiming that Sonic's attacks were completely ineffective. The scene shifts to Sonic attempting to escape the newly empowered Sea King. Sonic grudgingly realizes that his attacks have no effect, and he must retreat and find a weapon. Sea King clutches Sonic midair and crushes him, but it is revealed that Sonic ditched his clothes and escaped his grasp. The ninja assures Deep Sea King that the next time they meet would be his demise, and he disappears, leaving the monster alone.

Aftermath
Saitama sees Sonic and goes after him, thinking he's a civilian. The Deep Sea King senses the presence of multiple humans, and with sadistic bloodlust, goes to the evacuation shelter and attacks it. Afterwards, Sonic returns with a weapon and prepares to fight Deep Sea King once again, but finds that he's already been defeated, to his annoyance.

Trivia

 * ONE stated that Sonic with weapons would've defeated dry form Deep Sea King.