16-year-old Izuku stepped into his house, bags of groceries in each arm.

"Mom? Kacchan?" He kept his voice soft to avoid disturbing his 8-year-old ward, who, he supposed, surely must at least be resting his eyes, if not asleep, by now. "I'm home."

"Izuku." Inko appeared in the doorway of the kitchen. She looked as tired and troubled as she had before Izuku had gone out. "I'll put the groceries away, dear. You had better check on Katsuki-kun. He refuses to lie down and rest. As soon as you were out of the house, he got up and started to move around. I can't get him to listen to me."

Izuku wasn't happy to hear this, but he wasn't surprised, either. He set the groceries down, removed a jar of medicine from one bag and stuck it into his pocket. "It's okay, Mom. I'll. . .talk to him."

It's only been two years since Kacchan lost his mom and dad, and Mom and I haven't been his "family" for three months yet. For as long as we've known him, Kacchan's been angry and on edge. At first I thought he hated us. I could hardly blame him. If I were that little, lost my mom and had to live with strangers, I might hate everyone, too.

But now . . . I don't think Kacchan hates us. These days he usually listens to Mom and me, sort of, even though he isn't cheerful about doing it. He eats when he's told to and doesn't push our hands away when we tuck him in at night. Still. . .dealing with sick Kacchan is something else entirely.

As Izuku approached the door of Katsuki's bedroom, a guest room that had been converted for his benefit, he could hear thud-thud-thud-ing - the sound of tiny fists or a small, rock-hard head striking something. Well, whatever was being beaten clearly was not made of hard material, so Izuku didn't suppose he ought to worry too much. He placed his hand on the doorknob, but allowed it to linger there for a while as he stood outside of the door, considering what to do or say from here.

When we realized he was running a fever, we were terrified that it was something serious. We had to fight him to get him to the hospital. Kacchan was more afraid of going to the hospital than he was of the fever itself. He seemed to feel like no matter how sick he was, he couldn't really have COVID so long as he didn't have to hear a doctor say he had it. Thank goodness it wasn't anything as serious as that. He just has a bad stomach virus. He has to stay hydrated and stop exerting himself if he's going to get better. But he's being difficult about it - not because he hates us, but because he's scared of not being strong and in control.

At last, Izuku turned the doorknob and peered into the room. Katsuki was out of bed, surrounded by scattered blankets and pillows, pounding away at the punching bag that Izuku had given him as a present. Well, at least right now he was punching something that was actually meant to be punched. One or two of the pillows were far flatter than they had been when Izuku had left them, suggesting that they had taken beatings of their own earlier.

The small fists stopped flying when Katsuki took notice of Izuku's presence. He turned his head to regard the teenaged intruder with those flashing red eyes. The unruly golden hair was damp with perspiration, and the little cheeks puffed out, flushed with fever, exertion and frustration.

"It's good you're using the punching bag when you need it." Izuku shut the door behind himself. "But it's time to get back in bed, Kacchan." He unpocketed the jar of pills. "I brought you some medicine to help with your stomach pain. They're mochi-flavored pills. We'll start with two of them and then drink lots of water to get you cooled off."

Katsuki didn't make a move towards the bed, but his angry gaze drifted downwards. For a moment, he seemed to be considering whether he wanted to be cooperative right now. In the end, though, he decided against cooperation and scowled at Izuku again. "You think I'm some stupid baby who needs to take pink candy-flavored pills? Throw them away; I'm not taking those!"

Izuku winced inwardly. I guess I should have known he might complain about the color. He went over to seat himself on the bed. "I just thought you'd rather have something that wasn't bitter. Even I like having sweet medicine when I'm sick."

"I told you, I'm not sick!" As if to prove his point, Katsuki threw a punch at his bag.

"Kacchan." Izuku used what he liked to call his "Oniisan" voice - in other words, adopted as grave a tone as he was capable of using, which wasn't saying much. "I'm okay with you using the punching bag a little bit every day if you really need to. But if you don't stop overusing it, knowing you should be resting, I'll have to take it away till you're better."

The thought of being relieved of his beloved bag seemed to give Katsuki pause. Izuku, watching his facial expressions, saw at least three different questions go through his mind in the span of seconds. Would he really take my bag? How dare he even think about trying? Could I fight him about this? Is it worth trying?

At length, Katsuki did yield and push himself a foot or two away from the bag. He folded his arms. "Well, I'm still not taking your dumb pills!"

Are we really going to have a standoff now? Over the color of pills? Izuku could imagine that being sick and feeling vulnerable would make Katsuki more stubborn than he usually was, but even for him, refusing to take medicine that would help to alleviate his pain was extreme. He couldn't see that there was anything left for him to do now, though, but remain firm. When it came to nursing this child back to health, he could not afford to be overly-indulgent or play games.

"You don't need to take the pills right now if you don't want to, but you'll have to sometime today, before you eat anything."

"I don't want to eat anything," Katsuki muttered.

"You'll have to have some dinner. Mom will fix you some broth or something soft. For now, at least drink some water." Izuku patted the spot beside him. "Get back into bed. I'll fill your glass for you."

With a vicious kick, Katsuki sent a pillow flying. "Why don't you quit whining in my ear? I'm sick of lying around in bed, and I'm sick of drinking water!"

"If you're tired of drinking water, then you shouldn't have used the punching bag and made yourself hot!" Izuku attempted to reason with the angry, spiky-headed little bundle. "I know I'm being a pain, sweetheart, but I'm doing it because I want you to get better. At this rate, you're going to stay sick. How much fun do you think that would be? Just drink your water for me. If you can get through two glasses, I'll bring my TV set in here so you can watch cartoons until bedtime."

Izuku thought that what he was saying was reasonable enough. Somehow it seemed to incense Katsuki, however. The little boy got to his feet and stalked over, but not to sit down and accept a glass of water. He shoved a finger in the bewildered Izuku's face. "What do you mean, 'If I'm tired of drinking water, I shouldn't have used the punching bag'? You call yourself trying to discipline me like you're my dad or something? The hell do you think you are, Midoriya Izuku? You can keep your rotten punching bag; I don't want it. Take it and shove it up your ass! But don't you dare sit there and give me options like you're in charge of me. You don't tell me what to do!"

So saying, he snatched his pitcher of water from the nightstand and hurled it across the room, making sure to spill the icy contents over Izuku's lap and the bedsheets in the process. The pitcher did not hit the nearest wall and shatter, thankfully, but went tumbling onto the carpet. Izuku hadn't expected this outburst, and at first he couldn't decide how to react. Katsuki was looking him straight in the eye, and there was not a hint of remorse in his manner. To the contrary, after several moments of holding Izuku's gaze, he smirked as though to declare himself the victor.

Talking was not going to work with Katsuki; Izuku could see that now. Arguing and stubbornness were things that he might have continued looking for a way to cope with. Katsuki could not be allowed, however, to get away with physically-attacking another person, regardless of whether he did it with his fists or with iced water.

Izuku brushed the ice chips off of his pants. He rose to pull the bedsheets back and roll them down to the foot of the bed. When they were out of the way, he sat down once again and addressed Katsuki in an unusually-strong "Oniisan voice."

"If you don't want to drink your water, that's fine. Maybe you'll feel differently after I give you a spanking. Take your pants and underwear down and come here, Kacchan."

The smirk vanished. "After you what? What the hell are you talking about?"

"You heard me. Pants and underwear down. I'm going to put you over my knee and spank you for behaving the way you have."

Once again, Izuku saw several expressions cross Katsuki's face - one of disbelief, one of apprehensive comprehension, and his characteristic angry expression. Then his face hardened with truculent determination, and his hands formed fists. "I wish you would try it, you bastard!"

Izuku was going to nip this fist-brandishing display in the bud right away. "You're welcome to try to beat me up if you want to, but it won't end well for you. It would be best for you to get bare and come here so we can get this over with, Kacchan."

Slowly, the glint of "fight-readiness" faded from Katsuki's eyes, and his arms returned to his sides. He began to pay a great deal of attention to the carpet. Though he was still as tightly wound-up as an arrow string that was about to snap - Izuku could see that fact in every line of his body - he seemed to have given up any illusion that he could scream, punch or shove his way out of this situation.

"Fine," came the sullen, half-mumbled acquiescence after some time. "I'll drink the damn water."

"I'm glad to hear that. But if you're saying this to get out of a spanking, then it's too late. I'm realizing that Mom and I can't afford to go through this with every step we take to try and get you better, arguing with you just to get you to rest for a few minutes or take medicine that's good for you. You aren't getting out of this, Kacchan, so come here." Izuku patted his lap.

There was a lengthy silence, and then Katsuki's shoulders sagged beneath the weight of defeat. He came forward, one tiny step after another, stopping when he was at Izuku's knee. Izuku waited without saying a word until, with his face growing pink, Katsuki stuck his fingers into the waistband of his pants and tugged them down. They slid down at a snail's pace, as did his underwear afterwards.

Only then did he lift his head to stare Izuku in the face. His brow was bunched up in knots of anger, and his cheeks were flushed with embarrassment. But his eyes - his poor little eyes . . . Izuku could see tears glistening at the corners. Katsuki was scared.

Izuku picked him up and, turning him over, laid him across his lap. As he did so, he couldn't fail to notice how warm he was to the touch. He's burning up.

Katsuki lay as stiff as a board; regardless, Izuku shifted his body as well as his own thighs to ensure he was comfortably situated on his lap and his stomach was well-supported. The last thing that Katsuki's stomach needed was more disturbance than it was already experiencing because of his sickness. Izuku hoped that because Katsuki was so hot, being in contact with Izuku's cold, still-wet pants wouldn't be uncomfortable for him. He wrapped his left arm around his waist to keep him steady and in place, then rested his right hand on his bottom.

Izuku was not a very big or tall boy. But how small Katsuki's bottom looked, and how vulnerable, beneath his hand. He felt Katsuki quiver once or twice. Izuku didn't intend to cause him serious pain; he was so sick that he doubted he needed or could tolerate it. He only wanted to get and hold Katsuki's attention. In order to do this, he could not be gentle from the very start, so when he raised his hand and brought it down in the first spank, it was a very firm, resounding one.

"Gah-AHHH!" Katsuki jumped and attempted to bite back a cry of pain, but failed.

The smack had left its mark on his buttocks in the form of a bright pink handprint, the sight of which made Izuku feel a pang of guilt and a little stomach-sickness of his own. I've never spanked a kid before. I didn't expect it to be fun, but I didn't think about the fact I'd have to watch his skin get marked up under my own hands. Can I really do this?

He shoved his feelings aside. Either I do something or Mom will have to carry the burden. Even worse, neither of us will do anything, and Kacchan will keep running wild and hurt himself. With these thoughts, he lifted his hand again and delivered the second hard spank. This time, Katsuki did manage to stifle his cry. That was fine. Izuku didn't intend to try and force him to cry; Katsuki would only see him as a bully if he did. He delivered two more good swats before pausing to speak quietly to the figure lying on his lap.

"What you did was very naughty, Kacchan. I know you're in a bad mood because you're sick. You don't have to like everything that Mom and I ask you to do, and you don't have to pretend to like it, even though we wish you would be nice about taking your medicine and getting rest."

He gave Katsuki's bottom a firm slap. Katsuki, perhaps because it had caught him off-guard, did yelp at this one.

"But you still have to listen, especially when we're telling you to do something that's important for your health. It was wrong of you to throw the pitcher like you did. And it was wrong of you not to listen to Mom and to use the punching bag as much as you did when you were supposed to be resting." Another stinging slap, and Katsuki cried out again. "You already knew better, Kacchan. I know you did!"

By this time, Katsuki was squirming and shifting unhappily. The half-dozen swats Izuku had given him had turned his skin pink. Izuku would not need to give him anymore forceful swats. He brought his hand down on the center of his bottom, not hard enough to cause significant pain, but firmly enough to make noise, and felt Katsuki flinch. Yes, the sharp sounds of the smacks and the impact of his palm against already-smarting skin would do the rest of the work for him. Thus commenced a series of spanks, which came in one after the other with only short pauses in between.

"I'm disappointed with the way you acted, Kacchan. Up until this point, you'd been a good boy for Mom and me. I want you to be the good boy that we're used to having and take care of yourself without making a fuss."

POP. POP. POP. Little by little, Izuku's relative gentleness notwithstanding, Katsuki's bottom grew warmer and deepened in color. The little boy dug into the bed with his toes, then resorted to curling them to cope with his discomfort. At last, he succumbed to whining. "Owwwww."

Izuku heard tears in his voice. He couldn't stop now, though, not until he'd finished talking him. He moved his swats down to the undercurve of the bottom, causing Katsuki to buck against his grip. "This isn't fun for me, either. I just don't know what else to do to make you behave like the good boy I know you are. Mom and I've tried everything we could think of. I know we're annoying sometimes, though we don't mean to be. We only pester you and tell you what to do because we're your family now and we want what's best for you, sweet one."

Izuku began to smack the center of the bottom once again. A few spanks later, he heard a whimper, and his hand went still. After a moment's hesitation, he reminded himself that they weren't done yet. The smacking resumed.

"When your spanking's over, I want you to be ready to drink your water and take your medicine. If you decide you aren't ready, if you argue or won't cooperate, I'm going to ask you to bend back over my knee, and I'll spank you until I think you deserve another chance. I can promise you that when we're through, you won't want to argue with me a third time. Do we have an understanding, Kacchan?"

He received his answer in the form of a sob, the first one that he had heard so far. Katsuki's shoulders began to shake. From above, Izuku could see the gleaming of the tears that were making their way down his face.

"I'm sorry."

The words came out in a tiny voice, just barely audible. As soon as Izuku heard them, however, the spanking stopped. He helped Katsuki up, tugged his pants and underwear back into place, then settled him onto his lap. Katsuki fell forward and buried his face into Izuku's chest.

"I'm sorry," he quavered again and again between hiccuping sobs. "I'm sorry. . .I'm sorry. . . Izuku-niichan."

Izuku, who, out of respect for Katsuki's personal space, had only hugged him a few times before, wrapped his arms around the quaking little body now. He leaned in to press kisses to the bony blond hair and croon tender nonsense into the tiny ears. "Shhhh. Oh, I know. . . I know. I'm sorry, too. Calm down, sweet one. Deep breaths. Your niichan has you. It's all right now. . .you're safe."