One Punch Boss

Chapter 1

Saitama is going on a shopping trip in City D, his features relaxed into a derpier, non-threatening expression. He loved his city, but since he's literally the guy who runs it and made sure every monster followed the rules via the threat of punching, he was almost always mobbed with fans and paparazzi when he left his house. A guy just needs some time to just focus on the sales every once and a while. The peace didn't last long, because next thing Saitama knew, the place he'd been shopping in was stepped on.

Pulling himself out of the concrete he was embedded in, he checks around him and finds his flattened bag of groceries next to him. Good thing he hadn't paid for that yet. Checking himself over, he becomes fuming. "That son of a bitch wrinkled my suit!" Growling he looks up at the giant monster that interrupted his day off and has to shield his eyes from the sun because of how far up he has to look. Calculating the jump, he launches himself up the giant monster's shoulder.

Landing on the creature, he observes his behaviour for a second. What he found wasn't promising, with the big guy just muttering "I am the strongest man" over and over again.
He shouts at the guy. "Oi, big fella! You wanna put some pants on?"
The guy on the giants other shoulder notices the bald guy. "There's someone on your shoulder! Kill him!" What happened next surprised Saitama, which says a lot cause he's not really surprised by anything. The giant reaches up and swatted the guy on the opposite shoulder to Saitama like a fly.
Saitama's face reverts to its bland derpiness from the shock. "What?"

Apparently the monster is just as shocked. "BROTHER NOOOOOO!" Saitama covers his ears while his coattails flutter in the wind like a cape. "I ONLY WANTED TO BE THE STRONGEST, BUT NOW IVE KILLED MY BROTHER!" The monster grabs Saitama. "I BET THIS IS YOUR FAULT SOMEHOW! IM GONNA KILL YOU!" He tosses Saitama into the ground and starts beating into the floor, none of the blows actually affecting Saitama.
'This guy is clearly unstable, and stupid. Guess I'll have to kill him. But if I just punch him normally, he'll fall over and probably destroy most of the city and maybe it's neighbor. I'll have to make sure he doesn't land.' When the giant fists finally stop drilling him into the ground, Saitama uses his strength to launch himself from the hole and delivers a solid upward kick to the giants jaw, breaking his neck and killing him while sending the now dead giant into the sky where he disappears.

*elsewhere in space*

Boros pilots the ship that bears the pirate crew Dark Matter on his quest for his ultimate opponent. Geryuganshoop calls for the captains attention. "Uh, sir." Following the direction of his subordinates tentacle, he sees a giant creature float by their ship with grievous injuries to its neck and head.