Originally, one of the film producers, Takahiro Sato, intended to hire a Western musical act, namely Red Hot Chili Peppers or Lenny Kravitz, to record the themes songs.

An accompanying music video was directed by Higashi Hiroaki and released on Amuro's YouTube channel, showing the singer inside a large castle holding several corridors and mystical rooms.

In order to promote the track, "Fighter" was broadcast on several Japanese television shows and was included on the singers 2016–17 Live Style tour in Japan.

In December 2015, Amuro returned to releasing non-album singles with "Red Carpet", months after the distribution of her eleventh studio album Genic (2015).

[2][3] Following these singles were "Mint" (May 2016) and "Hero" (July 2016), two numbers that served as a television theme song, and the opening track to the 2016 Summer Olympics and Paralympics, hosted in Rio de Janeiro for the Japanese entry.

[4][5][6] A month after the latter song's release, Amuro confirmed her involvement with the Japanese drama–horror film Death Note: Light Up the New World, based on the anime and manga series of the same name, and intended for a late-October theatrical run.

However, knowing that the series was already popular outside of Japan, Sato decided to enlist Amuro in order to get the audience to recognized the "power of foreign artists" and also promote her work overseas.

The lyrical content delves into the point of view from the film's character, Misa Amane, whom serves as the accompanying female protagonist alongside Light Yagami, and is heavily based on self-empowerment and courage.

[12][13] During the second verse, the singer incorporates a rapping technique in comparison to the remaining parts where she sings, as noted by Japanese critic Kanako Hayawaka.

[1] Regarding the singles relation towards the film, Amuro believed that both "Dear Diary" and "Fighter" shared similar themes but were expressed in different styles of music.

The picture disc, featuring Amuro and the film's mascot character Ryuk, was published throughout selected Japanese retails and at her 2016–2017 Live Style concert venues.

Japanese critic Kanako Hayawaka enjoyed the track, commending its dance ready nature and production; additionally, she also highlighted Amuro's vocal performance.

[1] Similarly, an editor at CD Journal commended the dance nature of the song, and expressed delight towards Amuro's ability to continuously "update herself.

[28][A] Based on the first seven-days, the single entered the weekly chart at number three with 45,000 copies sold, making this Amuro's highest first-week sales since "Go Round"/"Yeah-Oh!"

[46] In an extensive analysis with Arama Japan, a staff member explained; The video takes place in a floating cubical fortress chained above a body of water.

For each chorus and other spontaneous intercut, Amuro and four background dancers perform in a grey-coloured ballroom, surrounded with black feathers, historical architecture and LED screens on the floor.

[50][51] Likewise, Space Shower TV premiered a music video special dedicated to the two singles and footage from the Death Note movie.