Sensei was warm.

Genos' hands were always too cold at first. Always. If he thought of it, he would have a mug of tea before bed. Just to hold it, really. Let the heat seep into his fingers. A few times, he ran them under the tap in the bathroom sink while sensei laid out the futon.

Most of the time, he took his warmth from Saitama.

Some nights it happened slowly, when the evening was marked by companionable conversation. The kind that started and stopped during dinner and continued a while later in bed. They lay side by side with their fingers twined together. Saitama would run his thumb across the hard ridges of his knuckles over and over. There was a tenderness to it, the reassurance that sensei liked being close to him, despite the strangeness. That Genos felt human to him. Slow nights were relaxed and quiet with drowsiness.

Sensei was warm, and other nights were quiet because Genos couldn't keep his mouth off of him.

Every part of sensei was a place to plunder heat, and Genos stole it in greedy strokes. With their chests pressed together, Genos on top, he could push his hands between sensei and the futon. Wriggle his cool fingers to burrow deeper and flatten his palms against the pliant smoothness of Saitama's back. He only protested the first time, and even then it was with affection in his voice. An amused whisper against Genos' lips.

He loved having sensei under him, between his legs. Fingers splayed on the firm heaviness of his chest, holding his balance when Saitama moved beneath him. Lifted his hips to shift their position on the futon. Lifted Genos, like his weight was nothing. When it was dark, Genos could sit back and gaze through his night vision.

It was only his hands. Even so, he resented it at first, the temperature difference drawing a bright line between them. But each time Saitama coaxed heat into the unforgiving metal, Genos minded less. There was no way his touch could pass unnoticed. Tracing the soft geometry of sensei's abdomen, the flex of muscle under skin. Dragging a thumb across his lips.

From his vantage point, Genos could look down at his own spread thighs and watch Saitama run his hands over them. Between them. Watch sensei's pupils dilate in the darkness and feel the thick rush of blood carried on his pulse.

"Hey," Saitama murmured. "Scoot up."

And without hesitation, Genos moved to straddle his head. To sink into the dark heat of his mouth with a groan.

Sensei was so, so warm.