As Ice by Ouvalyrin

Fugaku tells Itachi to expect a little brother and Itachi accepts, though later he wonders what he is supposed to feel. He has seen others interact with younger siblings, usually mocking or tormenting them in a supposedly familial, caring way, and he has seen them bounce off of each other and back each other up even as they tear each other down. Am I supposed to do the same? he wonders.

The idea is idiotic. Itachi cannot accept someone holding him back, and he resolves that his brother will be different. After all, he will be Uchiha. Itachi’s little brother, and if that does not make him special nothing will.

His mother - he never thinks of her by name as he does Fugaku, simply mother - tells him stories of him when he was a child, and he listens, quiet. He never spoke, he never cried, and his eyes were large and dark and they belonged to an adult - but she never tells him the last part, keeps it to herself, and Itachi can still hear her think the words.

Fugaku expects great things from Itachi’s little brother - there is no question that he will be a boy, for he is Uchiha and while Fugaku does not need another heir he wants boys, only boys - but it is a complicated pregnancy. Mikoto emerges weakened and sick, her breath rattling in her lungs. She drifts in and out of sleep for days, and by the time she holds her nameless son he has cried and wailed and slept and eaten. Itachi can see the surprise in her eyes at the wails and the soft joy he has never seen before, and wonders what makes his brother so special.

His heart clenches at his brother’s wails and he wants to hurt him. As an Uchiha he has no right to cry like that, no right to behave like that, no right to be a child.

“His name is Sasuke,” his mother tells Itachi. She keeps him close to her, as if unable to bear the idea of losing him, and Itachi holds his arms out. Silently, he demands his brother. Her fingers clench tight in the blanket for that one moment, clinging to Sasuke, but then she hands him over.

Sasuke looks like every other baby Itachi has ever seen. He is quiet, sucking on the corner of his blanket with more enthusiasm than proper, and he has a childish, innocent face. He gurgles and, with surprising speed, manages to wrap a tiny fist around a lock of Itachi’s hair. He hears his mother’s gasp, her hand covering her mouth, and she moves to take Sasuke. Itachi allows her to pry Sasuke’s fingers off - a good grip, he notes - but turns away before she can take him.

Sasuke laughs, and Itachi gives him back.

“He will be a good brother,” Itachi says and leaves. When he trains with Shisui later that day and the latter makes a remark about his brother, about why isn’t he there with the family, Itachi’s eyes reflect red.