"Mermaid" is the second single from Japanese pop singer Hitomi Shimatani's fifth studio album, Heart & Symphony, and her eighteenth single overall. "Mermaid" is described as a mixture between dance, pop, and has some presumably gothic undertones due to the "dark" sound of the song and the organ and harpsichord used in parts of the song. The b-side, 風の降る空 (Kaze no Furu Sora) is a symphonic ballad, incorporating a string section, piano, and an acoustic guitar. The single hit #18 on the Oricon charts and is reported to have sold around 20,500 copies.