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As far as stepdads go, Shouta supposes he’s lucky. The guy is genuinely nice, doesn’t force Shouta to take his surname, and is very obviously in love with Shouta’s mom. It’s that last tidbit that makes it completely unsurprising when they announce that Shouta’s going to have a new brother.
What is surprising is the sudden overwhelming feeling that rushes through Shouta’s veins when he cradles Hitoshi in his arms for the first time.
Hitoshi is small and squishy, and Shouta will go toe-to-toe against All Might for him.
*****
Shouta’s phone wallpaper is a photo his mom took of Hitoshi and him taking a nap on the sofa. Shouta had made a makeshift baby sling out of his capture weapon, decided moving to a bed was too much trouble, and promptly conked out.
Shouta absentmindedly pokes at his lunch as he looks at the photo, studying the pudge of Hitoshi’s cheeks as he drools all over Shouta’s shirt. The cuteness is almost enough to get him through the rest of the day.
“Yo, Aizawa! What’re you looking at?” Yamada leans over his shoulder and squints at Shouta’s phone. “Is that your brother? He’s adorable! Unlike you!”
All the energy Hitoshi gave him drains away as Shouta attempts to wrestle his phone back from Yamada.
*****
Hitoshi has developed a fascination for Shouta’s hair. He especially enjoys pulling it or worse, stuffing handfuls of it into his mouth.
Shouta can’t keep his Quirk activated 24/7 just to keep his hair out of the way, so he settles for a ponytail. Which Kayama apparently finds amusing, if the smirk on her face is anything to go by.
They’re standing outside of a convenience store, Hitoshi swaddled up against Shouta’s chest in his capture weapon, big eyes blinking sleepily—and suspiciously—at Kayama as she bends a bit to boop him on the nose.
“Hey there, big guy. You helping your brother with his errands?”
Hitoshi grunts and makes a grab for Kayama’s hair.
“No wonder you changed your hairstyle,” she snorts. “Oh, wait! I have an idea.”
Hitoshi looks like a very round purple pineapple when Kayama’s through with him, all of his hair gathered up into a tuft at the top of his head. Hitoshi actually seems pleased with the turn of events, arms and legs flailing as he babbles nonsense words at Kayama and Shouta.
“Well, look at you!” Kayama says. “It’s a good look, big guy!” She holds up a hand for a high-five. Hitoshi ignores it to grin at Shouta.
“Hmph. Seems like my charms are useless against the power of brother complexes.”
“Kayama.”
*****
“Can you say ‘papa,’ Hitoshi? Say ‘papa’!”
Hitoshi blows a raspberry.
“How about ‘mama’?”
Shouta watches his parents videoing Hitoshi and shakes his head. They can’t force these things. They should just let Hitoshi’s first word come naturally—
Hitoshi rolls onto his belly and looks around the room. “Sho?”
Shouta’s mom grabs his stepdad’s arm. “Ohmygod,” she whispers.
Hitoshi spots him sitting in front of the TV and starts crawling towards him. “Sho!”
Shouta’s face is completely pink by now. He picks Hitoshi up and tries to scowl at him. “Disrespectful. You should call me ‘nii-chan’.”
Hitoshi smacks his sticky baby hands against Shouta’s cheeks and laughs. “Sho!”
This is still Mr. and Mrs. Shinsou’s favorite home video years later.