How about Hairu delivering a little sister for Masanori when he’s four years old and she at first wants to name her Arimi after Arima but then Koori convinces her not to?

“Why is Mommy screaming?” Masanori shivers.

“Because Mommy’s getting you a little sister. The baby just need to move out her belly, that’s all.” Shio pats Masanori’s head.

Yusa closes his eyes and prays the kid asks no more questions.

But he wouldn’t be Masanori if he did. 

“How does it get out of her belly?”

“Auntie Eto can tell you,” Rikai says quickly.

—————————-

Hairu gasps as her daughter’s cry pierces the stale hospital air. 

Ui looks terrified as the baby is placed in his arms. He’s sure he’ll drop her. He can’t be trusted with something so precious.

“Arimi,” Hairu teases.

“Hairu, we settled on Miki.” Ui tightens his grip on their child. 

Beautiful story. Hairu smiles. “Just making sure you remembered.” 

“I think this kid has my hair.” Ui hands her to Hairu. 

“Masanori’s hair was dark, too. It just fell out and regrew pink,” Hairu mumbles.

“I can hope, all right!”

She giggles. 

“MOMMYYYYY!” Masanori flails into the room. “Mommy, Mommy, Mommy! Is this Miki? Can I hold her? Can she be my best friend?”

“Support her head like this.” Ui guide’s Masanori’s hands.

Masanori grins. “I’m gonna be the best big brother ever. Just like you’re the best mommy and daddy.”