Could it be possible that Pochita is the "Hero Devil"? It sounds absurd but think of all the heroic tendencies that Pochita possesses. He would always answer to cries for help as shown with Makima and Kobeni (even if he does accidentally kill the devils he helps because he wants to hug them), he seems to be pretty immortal as Makima states that devils would beat him but always return with a roar of his engine and we can even see him rip his out heart and regenerate very quickly from that heart, and there's the matter of his title "The Hero of Hell". Even his name 'Chainsaw Man' sounds like a superhero name and it's assumed that most devils call him that since both Yoru and Makima calls him that.

Now who would be afraid of heroes? Well villains would be afraid of heroes and the devils are this world's equivalent of a villain. He could be a special devil born from the fear that devils could have from heroic beings which could be why he has the special ability to permanently erase devils that he eats from existence. Hence, he's the devil that all devils fear the most. But why chainsaws? Well, it could be because chainsaws are an effective weapon to kill devils and also because of the rule of cool.

I know, "Just listen to the song" but I think it's a fun theory. That's why I think it's a half serious and half crack theory.