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 sister is a mess. I love her to death, but she is a mess.
There's nobody in the world that knows me better than my sister.
My first job is big sister and I take that very seriously.
Is solace anywhere more comforting than that in the arms of a sister?
Sister is probably the most competitive relationship within the family, but once the sisters are grown, it becomes the strongest relationship.