Spoiler Summary [Click to show or hide]:
OPM Manga Chapter 15.6 is a hiatus from the fight in Chapter 15 One Punch Manga Chapter 15.6 shows the young Saitama three years ago!
It was his first year of hero-ing and his hair was still intact. He was already defeating some monsters and saving ordinary people like a grandma who got attacked by a sunflower monster.
During this time, he was already well underway with his training regime of sit-ups, push-ups, squats, and jogging. In fact, it was his 300th day of training and his body was aching every time he almost completed his training for the day.
After saving a kid and a dog from getting hit by a car, a monster that looks like a boxer showed up. He identified himself as the Incarnation of Electric Light String and fought with the young Saitama.
Saitama got defeated with just two punches and after he thought it was all over for him, he stood back up and delivered a one-punch victory hitting the monster on its face.
Cut to the next page and Saitama is seen in his hero uniform, his head is bald, zero hair, and his face now looks like an egg. He continues to defeat monsters with just a single punch!
