To anyone other than Saitama, they wouldn't have heard it. Genos' machinery was flawless, he could be silent when he wanted to sneak up on someone. The sound of the machine whirring in him could be equivalent to the sound of the whirs a VHS tape made when it was recording. Saitama knew no one remembered how VHS worked anymore.

It occurred to Saitama that the sound got a little louder than usual at times. Saitama figured it was just Genos' machinery acting up. Maybe Dr Kuseno should get a look at it, he thought. Gradually Saitama realized that the sound only came at certain times. The sound was continuous, and resembled a gentle rumble. Like a big sized man with a huge mustache laughing and you're lying on his chest, listening to the sound of his laughter vibrating through his body.

Another thing about Genos was how he was warm. "It's my core," Genos had said, "it heats up, and I release the steam to cool it down." That was awesome.

During the cold days, Saitama had never used his heater as a means to save money. Besides, he had trained to survive even the coldest days to become a hero! With Genos around, Saitama would sit beside his disciple like he was a heater. It kept him cosy, warm and happy. Living with Genos did have its benefits after all!

"Genos, come here," Saitama waved him over and promptly placed an arm around Genos. It was colder than usual today, the snow falling outside in gentle little waves. He was already wearing several layers, but nothing beat having Genos close. It was like having a kotetsu.

"Sensei!" spluttered out Genos when Saitama decided to hell with it, and pulled Genos closer. There wasn't any other word for it, Saitama was cuddling Genos. His disciple was so warm! Saitama felt so cosy, and found himself yawning. Genos stared at Saitama with wide eyes. His body getting hotter by the second.

"Don't move Genos, I'm going to take a nap!" Saitama declared, manhandling Genos till they were both lying down on the floor close together.

"Y-yes sensei!" Genos said loudly before Saitama shushed him. His disciple was letting out steam from his body as well, heating up the room till it was the perfect temperature. Saitama would thank Genos later for being so considerate! Who knew the cyborg would be so useful in regularizing the temperature around him as well! Saitama laid his head on Genos' chest, over the core. He could hear the hum that the core made. It was so snug and toasty that Saitama fell asleep soon after.

When Saitama finally woke up to Genos lightly stroking his back, he noticed that the sound was back. That deep whirring rumble that Genos made occasionally. With his head over Genos' chest, Saitama finally realized something. It was as if Genos was purring! Genos' chest was shaking with gentle continuous vibrations.

"Genos, you're purring!" Saitama said with wonder. Genos became still, his hand warm on Saitama's back. The sounds became lower in intensity.

"I'm sorry sensei," Genos said in a low voice.

"No do it again," Saitama requested. "It's nice," he said happily. Saitama closed his eyes and didn't bother to scoot away. "Like a massage chair," he said, snuggling a little closer to Genos. The purring continued, and Saitama dozed off again. He stirred when he sensed Genos kissing him softly on his forehead. Saitama must be dreaming.

Ah, it has been so long since he felt this content and happy.


It's one of those things that Dr Kuseno cannot explain. He's tried to disable it, but he can't. So he leaves it be, it's harmless after all. Genos frowns and touches his core. "Can't it be fixed?" he asks Dr Kuseno.

"Maybe after some tests," Dr Kuseno says instead. As long as it doesn't affect Genos in battle it should not be a problem. Genos doesn't tell Dr Kuseno the real reason why he doesn't like it.

Genos nods, and heads back to his apartment.

"Yo Genos!" Sensei waves as he continues cooking. Sensei likes cooking sometimes, and Genos finds himself happy to consume food that sensei has prepared lovingly.

"That smells good sensei," Genos says. He feels content, and he can start to hear the whirring. He tries to calm his emotions again, taking deep breaths to sooth himself. The sound stops. Genos sighs in relief. He doesn't want to disturb his sensei's peace.

It is a hard task because sensei insists on being charming, amazing and utterly adorable. Genos cannot help the warmth that spreads throughout his system, nor can he stop the smile that often tugs at his lips when he is with sensei. Whenever he is happy, his core warms up, and he.. Whirs. Loudly.

Genos hadn't liked it. Sensei is the one who changes Genos' mind.

The turning point is when sensei holds him close during the cold winter nights and they sleep together in the same futon. Sensei says its to reduce the electricity bill, but Genos thinks its because sensei likes the warmth and company. Sensei said he likes it when Genos makes that sound as well, and hearing that made Genos happy, which lead to the sound getting louder as well.

Cuddles turn into long hugs, and sensei has taken to sitting in between Genos' legs when watching the television, his back to Genos' chest. He claims that it's soothing, to hear the sound Genos makes, and to feel the vibrations running down his back. He likes the warmth too, and Genos is content.

Genos starts getting bolder. He leans closer to sensei when they go out. His hand finds sensei's hand too, and the tight grip of their hands intertwined together makes Genos happy.

"Genos," sensei says one day, leaning his head back on Genos' shoulder. He's beside Genos, and Genos' hands twitch. He wants to just hug sensei tight and never let go.

"Yes sensei?"

"I'm going to kiss you now," sensei says, and Genos feels his core heating up rapidly. His eyes blink once, twice, and sensei smirks.

Before Genos can do anything, sensei has leaned in close and Genos can see every tiny freckle, and every eyelash. His senses become hyperaware. Sensei's lips are so soft, and he can feel sensei's tongue tracing his bottom lip. Genos feels as if he's going to explore. Sensei kisses him sweetly, gently, his hand stroking Genos' back. Genos parts his lips and the kiss turns hot and heady, wet and dirty all at once. Sensei groans, and Genos feels so tremendously happy that the sound gets louder and louder.

Sensei breaks the kiss, and he's nearly on Genos' lap, straddling Genos. Sensei laughs, his arm looping around Genos' neck. "Seriously Genos, I love it when you purr," sensei snickers. Sensei's eyes crinkle at the corners when he smiles at Genos. His body is warm, and Genos wants more.

Genos' face would heat up if it could, but he lets out steam in the room instead. Genos cradles sensei's face in his hands, kissing him, again and again, his lips brushing over sensei's eyelids, over his nose, the corner of his mouth. His core warms and warms, and he loses himself in the feeling of happiness.

Sensei laughs then, pushing Genos gently away before taking his hand and pulling Genos to their bedroom. "Come on you big cyborg cat," Sensei smiles fondly. "We're going to break in the new bed." Sensei smirks, and Genos feels as if his core would lurch out from how much joy he's feeling.

Oh. Oh.

Yeah. Genos couldn't be happier. He would purr for the rest of his life with sensei. And that wasn't a problem at all.