Incinerella was the nickname given to Genos by his stepfamily.
After the attack that left his own mother and sisters dead and Genos himself was grievously wounded, a mechanical genius by the name of Dr. Kuseno replaced much of his body with parts that looked as though they were designed for an automaton.
The gears had a tendency to overheat and incinerate anything nearby. His new stepmother wasted no time in replacing the items in their family home that had been so carefully stitched or embroidered by a member of said family (if occasionally with such epithets as, "Ella, age eight, made this and hated every stitch.")
Genos felt more guilt with every memory lost. He had already lost too many from the head trauma. He had stopped attempting to discuss the past with his father long before the man drank himself to death.
By the time the royal family celebrated their son's 25th birthday with (yet another) Engagement Ball, Genos was actually accustomed to his new life. He cooked, cleaned, and sewed for his stepsisters and stepmother ever since they had let the last of the help go, for want of resources (which they always seemed to find for new shoes.) Without his father bringing in money, they had only the estate to drain.
Genos rose every morning at dawn, swept the fireplace and set the kettle to boil. When his stepmother failed to replace the kitchen flint, he resorted to the heat from his own joints. Genos usually brought breakfast around midday, when his stepfamily finally arose. This gave him ample time to converse with the street rats while completing his chores. He had a special fondness for the ones with cleft chins or bowl cuts who couldn't beg a pittance from finer people. At least his stepfamily couldn't keep house well enough to notice the food that went missing from their pantry.
The morning of the prince's annual Engagement Ball was somewhat different in schedule. As every year prior, Genos woke his stepfamily at teatime, so they could begin preparations for the evening. These mostly consisted of ordering him about as he basted hems and ruched busts.
By the time they finally left, Genos was more than ready to sit on his stool and rest his residual limbs. He had absolutely no desire to stand up, let alone dance, but Dr. Kuseno chose that evening to pay a visit. He had been working on an upgrade ever since learning of his patient's incendiary troubles and had finally completed a set of new parts.
"There, my boy. I am so pleased to have completed them in time for the Engagement Ball. You can finally attend."
"But I never wished to attend," said Genos.
"Nonsense. How else are you going to get out of this hellhole?" asked Dr. Kuseno, with all the tact of someone too old to bother with it.
"I am fine, Doctor."
"You are up to your glass eyeballs in trauma, that's what you are. Go to the ball. Meet the prince. YOLO."
"What does that mean?" asked Genos, even as Dr. Kuseno removed a small brass box from his overcoat, pulled a lever, and propelled his patient via- Were those rockets in his feet?- towards the palace.
The rockets did not power down until Genos had blasted through the rather ornate front doors. With such an entrance, even the prince looked up. From the buffet table. Where he was stuffing chicken cordon bleu in his pockets, despite being the host.
Genos knew how to make a really, really good chicken cordon bleu.
The queen stood up from her throne at the front of the hall. "You!" she intoned. "Dance with my son."
"Yes, mamn," Genos said, more out of habit than anything else.
The prince did not seem overly enthused, nor much of a dancer. He kept stepping on Genos' toes. Fortunately, they were made out of metal.
"You look, uh, shiny," said the prince.
"Yes, mamn," said Genos, who was trying very hard not to incinerate royalty.
It didn't seem to be an issue. Even Genos had to admit his new parts were... beautiful. Silver to the point of being blue. The gears spun so smoothly, they could have been dancers themselves.
Unfortunately, they were still prototypes. His right foot fell off in the middle of a line dance. Then Saitama stepped on it. Genos did the only socially acceptable thing to do, which was speed-hobble towards the doors he had broken.
He did not expect the prince to follow behind, shouting, "Wait, you forgot your foot!" He was waving it over his head, apparently oblivious to the sparking wires.
Genos was starting to lose track of the socially acceptable thing to do. He spent most of his time with ugly kids and very mean people.
"Please don't hit me with it?" he tried.
The prince stopped short. "I'm not going to- uh, here?"
He handed Genos the foot.
"Th- Thank you."
"You know, whatever," said the prince. "Uh, I'm Saitama."
"Incinder- Uh, Genos. I'm Genos. I apologize for ruining your party."
Saitama snorted, most indecently. It was wonderful. "I think my party ruined my party. You might have actually saved it."
"I beg your pardon?"
"Just tell me this: If we stayed up all night talking, what would your top three topics of conversation be? Go!"
"Food, socialism, and justice."
Saitama looked taken aback. "Okay… That's better than bonnets. I- Uh, I mean… What kind of food?"
"I make a really, really good chicken cordon bleu."
"Sweet," said Saitama. "Wanna' get married? That socialism stuff sounds political, and you'd need a platform for that right?"
"Are you trying to extort me into wedlock?"
"I dunno'. Is it working?"
Genos took a moment to consider it. He may have also taken a moment to consider Saitama's muscles.
"Yes."
"Cool. Sorry in advance about my mom."
"My liege, you have no idea." Something occurred to Genos. "As a matter of fact, you may have met my stepmother and stepsisters tonight. They would be the ones dressed in ostrich feathers and nervous sweat."
"Oh, yeah." Saitama made a face. "I like your outfit better."
Genos took a moment to look down at himself. "My liege, I am not wearing anything."
"Call me Saitama," the prince insisted.