Chapter Text
This had been what Saitama was trying to prevent from the moment he, unwisely, allowed Genos to move in with him. Standing in the doorway, watching his (student? roommate? friend?) dip mechanical fingers into the long wooden crate full of dirt from the park in City Z where Saitama had died. When he looked up, saw Saitama frozen with his hand still on the knob, there was no surprise or fear in his eyes.
"I know, sensei." Genos dusted his hand off on his pant leg. He reached into his pocket and pulled out a box cutter. "I know what you are."
"Oh." Saitama shut the door behind him and slumped against it. "Okay."
He'd always sort of known it would end like this. The fact that it was Genos felt... right, somehow. The box cutter wouldn't be enough, it was too flimsy, and metal besides, but Saitama could let Genos pin him down and wait for dawn to do the rest.
He raised his eyes, expecting to see Genos in full battle mode, but instead saw him open the blade two clicks and put it to his own throat. "How much do you need, sensei? A little? A lot? Should I open a vein for you?"
Saitama sucked in a breath he didn't need and crossed the room so fast the breeze ruffled Genos' hair. He snatch the box cutter from his hand and held it at arm's length, the other hand gripping Genos' collar.
"Don't say that ever again," Saitama hissed. "I never want to hear you say something like that."
Genos was taller than Saitama. Not much, but he was taller. Here, this close, holding his collar so Saitama's knuckles brushed his skin, when Genos tilted his head back to expose the long line of his neck, Saitama's nose and mouth were in exactly the right position to lean in. He could smell it, thick and intoxicating, so strong he could almost taste-
Saitama dropped the box cutter and wrenched his unwilling fingers out of the crumpled fabric of Genos' polo neck. He felt his back hit the wood of the door, pressed his hands against it to ground him.
"Sensei." Genos took a step forward.
"Don't," Saitama said. His teeth had grown long and sharp, ready to feed, against his will, but he was used to them after two years and didn't lisp around the fangs. "Go away."
He didn't put any force behind it. Even if he wanted to, Genos was strong-willed and Saitama was weakened by these last couple months of inadequate feeding, he wouldn't have been able to compel him.
"You're blocking the door," Genos pointed out, mildly.
Saitama snorted. That was enough to break the tension, at least so he could move to the side, but Genos didn't show any signs of following the order.
"Sensei, let me help you."
Saitama shook his head.
"Use me," he put a hand to his chest, where Saitama could hear both the thumping of his heart and the low hum of the core that powered his mechanisms. "Bite me."
The hunger was so strong Saitama leaned forward, only his palms against the wall reminding him to keep back. "You don't know what you're offering."
"Explain it to me, then."
Instead, Saitama asked, "How long have you known? About me?"
Genos shrugged. He hadn't fixed his collar, and Saitama could see the mechanical protrusions stretching along his collarbone, reinforcing it to support his cyborg arms. "I suspected for some time, but I wasn't sure until last week. When your heart stopped beating."
"Ah." He'd been able to fake all the signs of life so long as he was well-fed, but that was the cause of the current problem too.
"What happened, sensei? Why did you stop drinking blood? If you need it to survive, if you're not hurting anyone permanently-"
"I didn't want you to know," Saitama mumbled. Louder, he added, "I thought monster blood was enough. It wasn't."
"And now?" Genos gestured at the window in the basement wall, at the patch job Saitama had done with scavenged wood and garbage bags. "You thought I wouldn't notice when you disappeared all day?"
"I don't know." Saitama shook his head again. "I was going to kick you out. I meant to, for a while now, but..."
Genos took another step. It was a small room, and even out of arm's reach he was close enough to smell. Saitama's mouth filled with saliva.
"I don't want to leave you, sensei. I don't blame you for what you are."
"A monster?" Saitama growled. He realized he was baring his fangs, going on the defensive.
"You're my teacher. Nothing's changed."
He took another step. Saitama's fingers punctured the brick of the wall.
"How much do you need?" Genos asked softly. "Will a little do?"
"A- a little would get me through the day." Saitama swallowed the drool before it spilled down his chin. "I don't need more than- than a bandaid's worth."
Genos tilted his head back. His neck was so long, so pale, Saitama could see the blue veins beneath his skin.
Saitama pulled his hands away from the wall. "If you want to leave after this... I won't blame you."
"I don't think I will, sensei." When Saitama stopped, he added, "But I'll think about it seriously."
"Okay." Saitama put one hand on Genos' hip and the other on his cheek. Genos leaned into it, closing his eyes, almost nuzzling his palm.
...Oh.
Saitama's nose brushed his neck, and he couldn't resist inhaling deeply, filling his lungs with the scent of Genos. Warm and sweet and rich, and for the first time Saitama didn't have to feel guilty about enjoying it.
"Okay," he said, mostly to himself, and plunged his teeth into Genos' flesh.
He tasted better than Saitama would have dreamed, if he'd ever allowed himself to indulge in fantasizing about it.
Then it was over, Saitama pulled back with an almost physical wrench of reluctance, licking his teeth to get every last drop. The wounds he'd left were small, barely oozing, but Saitama bit his thumb and swiped his own blood across them.
"It'll heal faster," he explained, though Genos didn't ask. He let out a breathy little sigh, contented, drowsy. It always made Saitama feel dirty when he did this to drunks. It didn't matter that there was no lasting damage, that he could wipe their memories of it, that he wasn't really hurting anyone. He felt like he was violating them. He felt like a monster.
Saitama patted Genos' cheek softly. "Wake up, you gotta get home and I gotta seal myself in before dawn."
"Is it really okay, sensei?" Genos asked. "Will you be okay?"
"I'll be fine. I can get through the day, and now that you know about it I can go back to feeding on humans."
"You could..." Genos reached up to touch his neck with thick fingers, just below the already-healing punctures. "You could keep feeding from me."
"You're not enough," Saitama said, chest aching. If he could... "And you don't want to get low. What if you get hurt in a fight and lose even more blood?"
Despite his training, it still happened sometimes. Saitama knew Genos hid from him how bad the damage was. How his cyborg parts kept creeping further up his body.
"But... once in a while would be okay, right sensei?"
Saitama bit his lip. His teeth had returned to a manageable size, passable for human. "Maybe."
Genos' face lit up, blushing pink, making Saitama's stomach clench. Guilt and desire and the sinking fear that he'd already gone too far. He wouldn't be able to stop now. He'd find justifications, he'd make excuses, he'd let Genos talk him into it.
But above even all that was the slow chill of warning that dawn was fast approaching, and if Saitama didn't get to safety he'd burn up in the weak rays that would manage to sneak through his attempt at blacking out the window.
"I've got to go, I've got to get in..." He gestured at the crate.
"A box of dirt? Not a coffin?"
"Never got properly buried. Nobody even knew I died."
"That's awful, sensei!"
Saitama shrugged one shoulder. "Not so bad. I got back up again." Genos was still looking at him with pity, so Saitama said, "Seriously I'm gonna get in the box now. You should go home, it's late, or early or whatever."
"But you're coming back?"
"Yes," he sighed. "Yes, Genos, I'll come home tonight."
Genos smiled. "See you tonight, sensei. Have a good rest."
"Yeah yeah."
Finally left alone, Saitama settled into the crate of dirt, a few minutes still remaining before he would have been in danger. The tiny bit of Genos' blood he'd drank had given him enough energy that he could have made it home if he ran, but he felt like it was better to stay here. Better to give them some space.
Genos had been willing to let Saitama bite him. Not just willing, eager. Had he known it would feel good? That that part of vampire lore was accurate? Or was he so devoted to Saitama that he really would open a vein if asked.
If Genos had cut himself, even a nick, Saitama didn't know if he could have resisted the temptation. He would have jumped on him, attacked him, buried his fangs deep and drunk his fill.
Genos was strong, a young man like him would normally be able to satisfy Saitama fully with no more than a few days of feeling weak and eating a lot of protein. But because he had less meat in him, he also had less blood. If Saitama gave in and took what he wanted, Genos might die.
Closing his eyes as he felt the chill of death overtake him, Saitama's last thought before dawn was that he was a fool for falling in love with someone who was in so much danger from him.
But then, that look on Genos' face when Saitama touched him, the way he nuzzled his hand... Not even Saitama could misinterpret that.
They said love made fools out of everybody.