"Amayo no Tsuki ni" was written by Shizuka Kudo,[3] under the pseudonym Aeri, and Hiroo Yamaguchi, who also arranged the track.

[5] Lyrically, the song describes a protagonist's proclamation of unwavering love to her companion, whom she vows to stand by through rain and thunder and be the "moon on a rainy night".

The song is composed in the key of C-sharp minor and set to a tempo of 91 beats per minute,[6] while Kudo's vocals span from G♯3 to C5.

Barks praised Kudo for the natural tone of her singing voice and for delivering an emotive vocal performance.

[5] The track received acclaim from CDJournal critics for its "simple and tight" sound and elegant string ensemble.