The story is a Coming-Out Story about Luna realizing he is transgender and coming out as as a stallion. It's also a Twiluna (or, Twilune) romance story.
Not to be confused with the Octavia/Luna fic Claro de Luna.
Clair De Lune provides examples of:
- Adaptational Gender Identity: Luna, canonically a cis female alicorn, comes out as a trans stallion in this fic.
- Coming-Out Story: Luna realizes he's trans, comes out as "Lune", and begins transitioning.
- Easy Sex Change: Equestria has magic that can permanently change a pony's anatomy.
- Queer Romance: Twilight and Lune stay in love even after Lune's transition.
- Rule of Symbolism: Downplayed. When experimenting with being a stallion by going to a bar with Rarity, Lune binds his wings down to ensure the integrity of his illusion spell (as he's disguising himself as a unicorn), reflecting chest binding.
- Shared Universe: Clair De Lune is set in the same universe as SPark's previous oneshots, Over A Cardboard Sea and Either/Or.
- Sobriquet Sex Switch: Luna changes his name to "Lune" when he transitions.
- Titled After the Song: The story is named after Claude Debussy's "Clair De Lune".
- Trans Nature: The "permanent magical transformation" support group in Ponyville usually acts as a transgender support group, however it is technically a support group for all kinds of transformations. One member is a unicorn, Green Wheat, who was born an earth pony. She felt uncomfortable being an earth pony so she turned into a unicorn. It's legal to change breeds, but there's a stigma against it.