Such a fluffy plotbunny I had running in my head for a while now. Enjoy.
Apologies for the OOC-ness. Updated to fix a few errors.
Bleach belongs to Tite Kubo

Ichigo Kurosaki had always imagined that his first child would be a son.

A wonderful boy who would carry his lineage with modest pride, growing into a man who would stand for justice in the world. A big brother to care for whatever siblings he had with a fierce determination- much like Ichigo himself.

Basically, he always thought that the new family they were starting would be a mirror of his own family.

Which is why he was slightly surprised when the doctors handed Rukia the baby, cheerfully saying "Congratulations, it's a girl."

He wasn't disappointed- far from it. It was impossible to feel anything but joy as he held the tiny child. Nor was he sexist- he cringed to image what Rukia would do to him if he ever thought of girls as inferior in strength.

He just hadn't been expecting to have an eldest daughter.

But looking down on the baby girl in his arms, he knew that she would be everything he could ever hope she could be, and more.

About five years later, Rukia and Ichigo were once again coming home from the hospital, a bundle of joy wrapped in blankets in Rukia arms.

"Rini?" She called softly. "Come here please."

The girl turned to her mother, her short, almost-black hair curling around her thin face. The girl came bouncing over, a familiar stuffed lion in her small arms.

"I'd like you to meet your new baby brother." Rukia said happily, showing the sleeping baby to the girl. "You're officially an older sister now. Isn't that great!"

She looked down at the small person, seemingly confused. "Brother?"

"Yeah," Ichigo said, kneeling down and placing a hand gently on the girl's back. "Don't be jealous if we can't play with you all the time now; we still love you very much. We have to take care of him and protect him until he's old enough to care for himself, okay?"

She cautiously approached the baby, who opened his eyes slowly. He reached out, his tiny hand closing around her finger. Then she turned to her parents, an adorably determined look on her face. "I'll protect him." she said.

Ichigo laughed, hugging his daughter. "I know you will, Ichiko... I know you will."

Rini - Little bunny (Rukia's nickname for Ichiko)
Ichiko - First Child

Thanks for reading!