summary: Sukuna tries to teach Yuuji self-defense, but of course, he happens to forget how helpless the toddler is.
cw: mentions of death/kidnapping, reader gets called helpless
wc: 1.4k
a/n: i love them so much. its so fun to write this au!!
big brother au masterlist
When you walk into the living room, you can’t help but smile. Truly, was it a rarity to see Sukuna and Yuuji getting along nicely. Of course, Yuuji was always sweet, but Sukuna was a brat and found that hanging out with a four-year-old was not really his cup of tea. Or at least, that’s what he proclaims to you.
Yuuji throws a punch at his brother’s hand, brows furrowing in concentration. Sukuna sits on the floor, cross-legged, and in front of Yuuji, who was standing at his full height. The older sighs, “Well, that was pathetic. Harder.”
The boy nods, obviously trying to hold back a smile. He wanted to seem just as serious as Sukuna did, but it was hard for the toddler due to how smiley he always seemed to be. But he lets out a tiny huff and brings his fists up to his face. Then, he makes a little “Hii-ya!” noise and slams his fist into Sukuna’s open palm.
“Okay, this ain’t working. Fuck, how are we of the same bloodline? I was not this weak,” Sukuna complains to himself, pulling his hands down.
You roll your eyes and step into the room. “Maybe because he is a four-year-old. Don’t think it’s his job to be strong,” You say, and Sukuna’s eyes flicker to you. A smile pulls at his lips, and the man begins to stand up from the floor to greet you. Yuuji beats him to it though, letting a high-pitched squeal in excitement before running over to you.
You grin at the noise, watching the boy waddle over to you with bright eyes. You crouch down to his level and greet him, ruffling his hair. Then you pinch at his cheeks, ignoring the whine of complaint from Yuuji. “You are way too cute to fight! Huh, no fighting for you. You just gotta stay this small forever!” You coo, peppering kisses to the boy’s cheeks and forehead.
The boy lets out a fit of giggles and a “Noooo! Wanna be big like Kuna!”
You shake your head, a fake pout on your face. “But Sukuna isn’t cute at all,” You half-heartedly complain, sparing a glance at your lover.
He walks up to the two of you and picks up Yuuji by the back of his hood, causing the kid to squirm in the air. Sukuna pays no mind to it, instead looking toward you, who is standing back up. “Don’t lie,” He scolds, and you raise your eyebrows, “I am adorable.”
You chuckle at him, rolling your eyes, and he in return presses a quick kiss to your lips. His brother begins to whine in complaint, causing the older to roll his eyes. “Yeah, yeah, quit whining. I’ll put you down in a second, little pest, but you need actually to put in some effort to fight me.”
“Okay!” Yuuji exclaims, and Sukuna sighs. Yuuji was so agreeable. When Sukuna was that age, he was supposedly a brat who argued with everyone, or at least that is what he had heard. Yuuji was strangely different than him. He didn’t know if he minded it or not.
Sukuna puts the boy down and sits again on the floor. He glances at you, who is taking a seat on the couch. Your eyes seem to read, play nice. It makes Sukuna want to roll his eyes, but the kid distracts him again, his tiny hands placed on the knees of Sukuna’s sweatpants while he grins up at his brother. The little beast had no concept of personal space, and the older of the two swears he can feel his brother practically breathing on him.
Sukuna pushes the boy off, sending him falling on his backside. “Sukuna,” You warn, but he ignores you. Yuuji only frowns and gets back up again, climbing back over to the other.
“Pretend im a kidnapper,” Sukuna demands, straightening his back and moving closer, taunting the small boy. “I am a very bad man who is going to take you home with me and lock you in my–”
“Sukuna!” You interrupt before Yuuji could hear his brother’s unneeded explanation. Yuuji seemed to stare owlishly at his brother, a little nervous but mostly confused about what he was talking about.
The man grins at you and shrugs his shoulders. But he abides to your wish with a scoff. “...Do bad things to you,” He weakly finishes. “Now, defend yourself!”
Yuuji’s hands go up into his mouth, tiny fingers playing with his lips, and he shakes his head with a giggle. “But big brother will protect me!”
Sukuna pinches the bridge of his nose, and you let out a small laugh. “I’m dead.” Yuuji’s face visibly falls. “The kidnapper killed me because you were too weak to defend yourself and save me. Now look, Y/N is all alone and helpless because of you.”
Your mouth opens in shock at the bluntness of it all. Yuujis eyes are wide, and he goes silent for a second. Then, his mouthline begins to wobble, and his eyes begin to water. “Kuna gone?”
Sukuna begins to backtrack, not wanting to deal with his brother’s tears. He stumbles toward the child, eyes wide. “It’s a hypothet–”
Yuuji’s scream sends you scrambling to your feet and over to the pair immediately. You grab Yuuji by the waste and swing him around, a huge, forced smile on your face. “And boom!” The force of it all startles the small boy, and he pauses his cries for a moment with owlish eyes while you continue to swing him around. “Y/N comes in and saves the day! And guess what, Sukuna was just sleeping!”
You place Yuuji on your side and help wipe his tears away. Only about two or three fell before you grabbed him, but still, his eyes seemed to be slightly puffy. The boy continues to sniffle, hands rubbing at his eyes. “Just sleeping?”
Before you could answer, Sukuna tears the boy from your arms. He holds him up in front of him by both of Yuuji’s underarms, causing the boy to dangle in the air. “I’m offended that you would think I would die so easily, brat.”
A smile begins to crawl up Yuuji’s face, but he shakes his head, and his voice holds a whine to it. “Don’t. Don’t like it.”
Sukuna sighs before placing the boy on his hip. Yuuji seems to find comfort there, burying his head into his brother’s shirt. It was rare to be held by Sukuna, and Yuuji obviously wanted to soak up all the time he has up there. “Yeah, I don’t think I would like being dead either. Luckily, your brother is the strongest, so you won’t have to worry bout that, yeah?”
Yuuji nods into his brother’s side, grinning and possibly wiping snot onto Sukuna. You take this time also to add your say in the matter. “And I’m not helpless.” You glance at the man who was just remembering what he said in the moment.
“C’mon, maybe just a little?” He teases, and you step closer to the pair, fighting back a smile. But before you could retort another teasing bite, the boy interjects his opinion.
“Nuh-uh! Y/N saved us. You sleeping, Kuna!”
You fake gasp in realization of his words, and Yuuji’s eyes light up. “Oh my, you are so right, Yuuji! Don’t you think he is the helpless one?” You coax, and Yuuji seems to lean toward you at your excited tone.
He nods his head rapidly, not really knowing what he is agreeing to but just trying to mimic your actions. “Kuna helpless!”
Sukuna rolls his eyes at the two of you and pinches the boy’s cheek, looking down at his brother. “Says the one who had a whole breakdown over the word–”
“Sukuna.”
Sukuna takes a deep breath and glances at you and Yuuji’s big dark eyes. He shakes his head in defeat, “Yeah, guess I am, ain’t I?”
You crack a smile, and Yuuji squeals in delight, digging his tiny hands into his brother’s shirt. Sukuna ruffles the boy’s hair.
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