The story begins when Celestia and Luna go to see a concert at the Canterlot Philarmonic. While there, Luna becomes enamoured with a cellist named Octavia. After meeting back stage, the two hit it off quickly. They go through various trials and hardships through their relationship, but eventually the reality of the differences in mortality come to limelight.
Written during the hiatus between season 1 and season 2, the fanfic has several inaccuracies compared to later episodes. Neither pony had much characterization in canon at the time so fans made up their own. Luna in the fanfic is shy and somewhat awkward, as was commonplace in fanworks at the time, and is in her original pilot design.
Claro de Luna provides examples of:
- Affectionate Nickname: Luna calls her sister Celestia "Celly" and her lover Octavia "Tavy".
- Career-Ending Injury: After Octavia develops arthritis in her hooves, she can't play the cello anymore. She opts to become a composer.
- Disabled in the Adaptation: Octavia is mute due to a childhood injury. In canon, she was later shown to be able to speak.
- Furry Reminder: Octavia met Luna when she was 6 years old and died of old age at 26.
- Local Hangout: Visiting Pony Joe's Malt Shop is a reoccuring theme in the fanfic. Luna and Octavia go to it for their first date.
- Love at First Sight: Luna falls for Octavia the second she lays her eyes on her.
- MayflyDecember Romance: Luna is functionally immortal while Octavia is just a normal pony. It's even more pronounced as, in this fanfic, ponies have lifespans comparable to real horses and rarely make it past 25.
- The Speechless: Octavia can't speak due to a throat injury received as a foal. She communicates through sign language.
- What Beautiful Eyes!: Octavia's purple eyes get noted several times. The story even begins with Luna having a prophetic dream about them, even before meeting Octavia.