While the prisoners of Smelly Lid Prison attack Puri-Puri Prisoner, Nyan comes in from behind the hero. Nyan tells him that once someone becomes a monster, they can never go back.
Before Puri-Puri Prisoner can even react, Nyan slashes the hero across his chest with minimal effort, yawning in the process. He attacks the hero again with his Feline Retribution, drawing up large portions of blood and ripping Puri-Puri Prisoner's sweater apart.
As Puri-Puri Prisoner evolves during the battle and attempts to forcibly shower the prisoners with love, he begins to feel uneasy. This is because he was once a house cat, and his former master would constantly shower him with unwanted love. Not wanting to deal with a similar foe, the monstrous cat decides to retreat and manages to slip through the crack of the wall. Puri-Puri Prisoner doesn't understand how Nyan could do this, and the monster replies by saying he can pass through any gap larger than 3 millimeters, and since there are so many cracks, he can easily travel around the headquarters.
Despite his retreat, Puri-Puri Prisoner does not allow Nyan to run away like this, and so he decides to increase the power of his vibration with his bristle armor on his forearms. The hero dives into the concrete like a swimmer and uses his Angel ☆ Crawl to chase after Nyan. Nyan notices this and enters another crack in an attempt to lose the hero. Alas, Puri-Puri Prisoner is still determined to chase him to the ends of the Earth and catches up with Nyan. They come across the prisoners again, with one of them asking Nyan if he killed Puri-Puri Prisoner.
From above, Puri-Puri Prisoner comes crashing down, and he accidentally crushes the prisoners and kills them with his Angel ☆ Crawl. Puri-Puri Prisoner mourns the death of his fellow prisoners, but quickly focuses his attention on Nyan and he prepares to fight the dragon-level monster and avenge the deaths of the prisoners.
However, by this point, Nyan has already retreated outside of Puri-Puri Prisoner's vision, going to search for other heroes to fight. Puri-Puri Prisoner does not get this, however, because he is the weakest of the S-class heroes, and as he walks through the headquarters to search for more monsters, he states that Nyan will regret fighting whichever hero he comes across next.
After Nyan retreats through the cracks of the headquarters, he comes across Saitama and attempts to strike him with a surprise attack. However, he's shocked to realize the attack had no effect, and immediately retreats again.