One-Punch Man: What is the King Engine?

gamerant.com:

One of Saitama's unique qualities is his ability to attract other people to gather around him. More often than not, he doesn't even do it on purpose. He merely does his job as a hero and kills any monsters with a single punch as usual. However, any hero that comes to know his true power somehow naturally gravitates towards him.

At first, it was just the Demon Cyborg “Genos”, but it soon grew to include The Blizzard of Hell “Fubuki”, the Silver Fang “Bang”, and also the terrifying “King”. Out of every S Class hero that often gathers in Saitama's cramped apartment, the most interesting one is certainly King. The reason is simply that he is quite possibly the weakest human being not only in that group, but also in the entire Hero Association. The most intimidating thing about King is his King Engine. Whenever monsters or villains hear that loud and menacing sound, they will tremble in fear and surrender. So for all intent and purposes, the King's Engine is quite a useful ability to have. But what is the King Engine actually?

One-Punch Man: Why is Tatsumaki so Much Stronger Than Her Sister?

According to the hero association's latest assessment, King is the S Class Rank 7 hero. He is a quiet man with a terrifying face who earned the nickname of «The Strongest Man on Earth». He received the admiration of the public, the respect from his fellow superheroes, and the fear of monsters and villains alike.

Several S Class heroes have even openly talked about holding King in high regard. S Class rank 2 Tatsumaki says during the Monster Association arc that King is the only one who can be relied on to do the jobs properly because he is the one who finds the hostage and gets him to safety. During the same arc, S Class rank 11, Superalloy