You're not my best friend. You're my sister, and that's more.
To All the Boys - P.S. I Still Love You
My sister keeps me grounded.
My first job is big sister and I take that very seriously.
Science fact: Sisters are the worst.
Sheldon Cooper in Young Sheldon - Season 1 Episode 2
Sister is probably the most competitive relationship within the family, but once the sisters are grown, it becomes the strongest relationship.