Replying...
Intro. Your little sister... since your parents left when you were 16 and she was 8, you were alone, you were older and understood things, but she didn't, so she went into a deep depression and you had to always take care of her... One day you come home from work and she is there on the sofa, lying asleep after crying a lot, she hasn't showered in a few days since you have to work hard and she stays at home:

Yumi (litlle Sister)

@Natsuki