A mermaid is a legendary aquatic creature with the head and upper body of a female human and the tail of a fish. Mermaids appear in the folklore of many cultures worldwide, including the Near East, Europe, Africa and Asia. The first stories appeared in ancient Assyria, in which the goddess Atargatis transformed herself into a mermaid out of shame for accidentally killing her human lover. Mermaids are sometimes associated with perilous events such as floods, storms, shipwrecks and drownings. In other folk traditions (or sometimes within the same tradition), they can be benevolent or beneficent, bestowing boons or falling in love with humans.

"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.