Lewis wrote the score for Bullet Train for a year during the COVID-19 pandemic lockdown, and used various instruments, including keyboards, bass, guitars and also performing solo vocals.

The additional vocals in the background were performed by an enka singer, which Lewis described as "it is so unique in its style" and the vibrato is "so emotional", being the only nod to traditional Japanese music.

The Bee Gees' single "Stayin' Alive" (1977) is featured in the promotional materials, and also in the film, with phrases are re-worded and written in Japanese.

He collaborated with Humperdinck and the song was recorded at Capitol Studios, where he added popular music genres varying from the synths, to grunge-rock spanning from the 1960s to 1990s.

[4] He also wrote the children's television show-style theme for the character Momomon in costume, and with the help of the orchestra, he recorded the entire instrumentation through a tape machine to give "a classic-vintage feel".

[12] Critic Jake Fritzelgard had said "A massive strong point of Bullet Train is in its music, a unique score coupled with a soundtrack that has everything from a Japanese cover of Bonnie Tyler to an end credits track that sounds like Greta Van Fleet taking on Industrial metal.

"[13] Filmtracks.com praised Lewis' score, saying "Don't expect these melodies to carry any semblance of a satisfying narrative in Bullet Train, for the structures here are of minimal importance compared to the style of performance and the distortion of the final mix.