A heavily hip-hop and EDM influenced release, NCT #127 had the participation of the production team LDN Noise, Tay Jasper, Ylva Dimberg, Chris Wahle, Andreas Öberg, Timothy 'Bos' Bullock, Adrian McKinnon, MZMC, The Colleagues, Double Dragon, and others for both lyrics and production, while SM's founder, Lee Soo-man, was the EP's executive producer.

The initial line-up consisted of the four aforementioned members from the previous sub-unit NCT U, Taeil, Taeyong, Jaehyun and Mark, and three new members who were SM Rookies: Yuta, Haechan and Winwin, with the latter having appeared as a dancer for the live performance of NCT U's "The 7th Sense" during their first live performance at the 16th Music Feng Yun Bang Awards in China.

The album's lead single, "Fire Truck", was described by the label as "a perfect summer tune under the Moombahton genre" with elements from hip-hop and trap music.

The last track, "Switch", is a tropical house song performed by the members in the SM Rookies Show previously in 2015.

Following the announcement of their first release, the group unveiled the music video for the lead single "Fire Truck" on July 8, 2016.

[8] A music video for the track "Switch" was released later in December 2016, with footage recorded in 2015 and fshowing all of the confirmed SM Rookies trainees at the time.