The animated film Fureru, directed by Tatsuyuki Nagai and written by Mari Okada, was first announced in December 2023.

[3] Nagai revealed in the press release that he believed only Yoasobi could create music with unique lyrics that really "touches" people's heart.

[6] Shortly after the program ended, Yoasobi announced that the song would be available for digital music and streaming platforms on October 1, the duo's fifth anniversary, as well as the English version the next day.

"[11] According to Yoasobi, "Monotone" was inspired by the "relationships between people" depicted in the film, expressing loneliness and feelings of missing someone in their own life.

[13] Tomoki Takahashi from Rockin'On Japan described that the song's "oriental and rhythmic melodies create a cheerful, yet sad, insane sentiment that even exudes a sense of mystery.