Once, Princess Celestia and Princess Luna ruled Equestria together. However, Luna became disillusioned with the lack of love she received from ponies, who adore Celestia's day and shun Luna's night. She decided to attempt to leave Equestria to create her own Lunar Republic, an action that amounts to treason against Equestria. Now, Princess Celestia must administer the proper punishment to her sister, even as it tears her heart in two.
An alternate version of Luna's descent into Nightmare Moon.

An entry in Imposing Sovereigns III, using the prompt Celestia/Justice.