Cliché #104: the bad boy/MMC has a younger sister that he cares for a lot and the FMC is smitten upon seeing his "soft side"

"This is my sister, Cynthia," Matthew said, gesturing to the little girl standing in front of me.

I swooned as he picked her up in his arms, kissing her playfully on the cheek. "How have you been, you mischievous monster?" he asked, swinging Cynthia around, causing her to shriek in delight.

Omg, this is such a cute and rare sight! Even though Matthew has been acting like a moody bitch around me for the past few days, I love this side of him and want to marry him! Ugh, a guy good with kids is sooooo hot!1!!1!1!1!1

Calm yourself, damn