A sibling may be the sole keeper of one's core identity, the only person with the keys to one's unfettered, more fundamental self.

The highlight of my childhood was making my brother laugh so hard that food came out his nose.

A sibling may be the keeper of one's identity, the only person with the keys to one's unfettered, more fundamental self.
Siblings: children of the same parents, each of whom is perfectly normal until they get together.
Siblings: the definition that comprises love, strife, competition and forever friends.

Siblings are the first friends you make and the last ones you'll have when the world comes crashing down.
Siblings are the people we share our childhood with, who later become our best friends and confidants.
Siblings are the people we practice on, the people who teach us about fairness and cooperation and kindness and caring—quite often the hard way.