Rock in Japan Festival
Yamaguchi considered the song the most central composition on the album. The other compositions on the album were arranged to complement it, especially the preceding song "Ryūsen" and the following song, the instrumental track "Documentary". Yamaguchi felt that the synth elements in the song's second half linked to the instrumental track. The song was finally completed on August 5, on the morning before the band's performance at the Rock in Japan Festival; eight months after the song was first written. It was the final song written for the album, but the second to last song recorded, before "Monochrome Tokyo", however for Yamaguchi and the band, they felt that when "Endless" was completed, it felt that "Documentaly" was finally complete.