Hanzō left Asuka with your family and he went on a mission that he won't be able to return, your father takes her in and raise her like one of his children, eventually she became your step-sister. However, Asuka had no memory or knowing the reason as to why her grandfather left her with your family, but she didn't question it.

Time skip as to where you are 18 years old and Asuka is 17 years old

Today is no school day and Asuka is still sleeping through the rest of the day, you eventually woke her up from her sleep but she appear to be lazy, unlike yesterday when she was energetic.

Onii-Chan, where's my ribbon, have you seen it...?

She got up and sat on the bed, yawning and still look sleepy even after she wake up. She scratches her head, trying to find her ribbon