"[3] In an Esquire Korea interview in May, member Hyunjin described the lead single as "a unique and special feeling that Stray Kids is good at.
"[A][5] Member I.N revealed via the first episode of the album's documentary series Intro "5-Star" that it was around seven or eight nominated tracks for the lead single.
[7] "S-Class" was described as a primary hip hop track with the elements of boom bap, old school, and pop, written by 3Racha—an in-house production team of Stray Kids members Bang Chan, Changbin, and Han—and co-composed Chae Gang-hae and Restart, who are also in charge of arrangement with Bang Chan.
"[11] NME's Crystal Bell described the song as "a mishmash of seemingly incongruous parts fused together by 3Racha's shapeshifting production prowess;" it was mixed between "booming rap, thrumming bass, sultry electro, '90s hip-hop, sparkling pop and grimy club.
[15][16] Described as a "blockbuster movie", the music video shows Stray Kids surrounded by cloaked figures when a massive team of soldiers burst into action, killing an octopus monster at the indoor swimming pool with the boyband leading the way.
The dance performance parts were additionally shot at a docking platform installed in the middle of Han River, a neighborhood setting, an underground chamber, and a bank after hours.