From Video Game Music Preservation Foundation Wiki
Lunate Elf is the theme for Stage 2: "Lake Elf ~ Water Magus". This song is track 4 in the music room of the game.
ZUN's comments about the song in the music room:
And in the omake that sits in the game's main directory:
- Japanese: ルーネイトエルフ
- Romaji: Ruuneito Erufu
- Translation: Lunate Elf