It is the fifth single from their sixth studio album The Side Effects, produced by Michael Baskette, written by Masato Hayakawa and Ryo Yokochi, and was released on 2 November 2019.

[3] Due to the success of the single being on the anime, it started rotating in circles around the metalcore scene elevating the band to new heights.

[5] At the end of the following month on August 26, it was announced that "Mayday" would be selected to be the second opening for the anime Fire Force.

[6] The guitarist and one of the main songwriters, Ryo Yokochi, would go on to explain the process and collaboration of working on "Mayday" for Fire Force: "When we got to talk, we got asked for permission, and we were sympathetic to the information that Mr. Okubo often listens to loud music in the early 2000s, and because it was a thing with hope for offensive music, we tried to do it with all our best, the dark side of the original (Shin).

[10] In an interview with Gekirock, Hayakawa would go on to explain the reason for the collaboration with Crystal Lake's, Ryo Kinoshita, on "Mayday" and the decision for having the song being the opening track on The Side Effects.

Suzuki Kayomi of Live Japan Music wrote: ""Mayday" opens the album featuring Crystal Lake singer Ryo Kinoshita, a partnership we had long known when Masato Hayakawa appeared on the single "The Circle".

[14] In 2022, Comic Book Resources named "Mayday" as the sixth best anime song to "add to your workout playlist.

The music video is directed by Inni Vision, with footage of the band captured performing "Mayday" on their One Man Tour in Japan.

In late November, "Mayday" overtook "Die Tomorrow" to become the most-viewed song by the band on the site.