My Little Pony: Friendship Is Magic (2010)

S07E10 A Royal Problem

Starlight Glimmer is dispatched to mend a rift between Princess Celestia and Princess Luna. As she delves deeper, she discovers that the root of the issue lies in the sisters' lack of appreciation for each other. In a moment of recklessness, Starlight decides to swap their cutie marks, hoping to teach them a lesson about understanding and valuing one another.