He could not believe his eyes, and descended into a state of panic, as his breath hitched and faltered. The gruesome scene he had found before him, it could not possibly be real.
Doctor Kuseno, Genos' savior and father figure, limp in his office chair, the scent of blood flowing thick from the grotesque display. His body was nearly shredded, though limbs were left attached, and the sound of half-melted metal sizzling through dead flesh remained under the gentle crackle of dying fires.
Saitama almost retched, falling down onto one knee and clutching his stomach.
"How... could he...?-"
The sound of heavy footfalls made him start. His head whipped around to look behind him, almost quickly enough to bring on his gag reflex again. And there stood the beast, positively gloating from pure joy. The demon that, with utmost glee, had brutally choked poor Mumen Rider to death with a tire from his own mangled bike.
"Ah, it seems so my surprise was compromised. Either way, allow me to explain this piece of intricate art to you, dear Teacher of mine. I had no use for a mortal by my side, I am sure you understand. If nothing could ever break me, why would I require repairs? I covered flesh and bone in a titanium overcoat, a relic to endure the weight of time. The good doctor would have eventually died, lost to the void of the past. And as you know, dead things rot. Everything but you and I, for I am a monster, and you are a god."
The villain smiled. As much as Saitama wanted it now, he could not will his mind to contort the handsome face of his foe into something hideous. That smile. It wasn't a grin or smirk. Just a smile, a warm, pretty smile. A typical 'Genos' smile. The murderer, Genos, smiled at him. Genos...
The hero was furious, at himself, at fate. Genos had become this for his Teacher, who could not bear the thought of having to kill this cyborg, even after losing everything else to him. His home, the Hero Organization, all his friends, and his good, beautiful, Hero-disciple.
'This isn't Genos.' The bald hero tried to tell himself, still not convinced even after all the slaughtering the monster had done, gleefully painting the world red at a merciless pace. It was Genos, in a sense. He admired and praised his Teacher whilst ripping a gash straight through Metal Bat's chest. He smiled his old loyal smile, only ever seen by Saitama, when he was happily chipping away at Drive Knight’s shattered pieces, assembling them to himself as if by magic.
"Things are prettier when they burn. So it is with trust, too. Could you recall a time where you felt more emotions than now...? I strongly doubt it. You are welcome, Saitama-sensei."
It was Genos, in every way, simply lacking restraint, and his humanity. His rage was free to lash out at the world, the world he so despised. He had always looked forward to ravaging everything it stood for, but back then, he was still too weak, too much like a 'Hero'. He would kill all the rest of the world, civilians, Heroes and Villains. Just to ensure the Caped Baldy belonged only to him.
"Loneliness makes way for madness. Won't you dance with me among the dead? I rolled out the red carpet in preparation for your arrival. Nothing will withhold either of us from saying what must be said, this time. There is no longer a Hero Association to drag you away from me for weeks upon end. No more old friends with whom, instead of me, you spend the tiniest shreds of spare time. Fight me, beat me. Face me, stay with me. Please, something. Anything."
Saitama knew Genos did not want his love returned per se, but merely ensure his own feelings were clear as day. Genos would just keep killing so joyfully, and Saitama would always be trying to stop him. They could fight for the rest of eternity, on a dead world with blood-soaked soil.
The cyborg reached to his unclothed super-alloy chest plating, ripping away a piece of the outer shell of his armor. A bold, so very 'Genos' move, the monster so familiarly unafraid of the risks as he exposed the source of his power.
A dark, corrupt core pulsed within his core compartment, a fractal of an ominous black shine radiating out. Tiny, black, insect-like arms reached out from the cavities of his body in an attempt to grab a hold of and re-fit the plate he had so violently yanked out of place. He was nothing human. It was all gone, a shell, a beast.
"Never in my past had I foreseen it would come to this. I am a god-level threat. Not even Metal Knight could dent me."
He grinned maniacally then, digging into his core port and pulling the evil orb out of the harness. He smiled, more joyful now than Saitama had ever seen him in the past.
"I am not afraid to reveal my core to you, for I know you will never have the heart to break mine."
He smirked and slotted the core back in place with practiced ease, content to watch the desperate, fearful tears of his teacher, Saitama, the Hero named One Punch Man, the number 1 S-rank.
"I love you, Teacher."
Saitama had never felt so weak.