NCT U are a South Korean boy group formed by S.M. Entertainment in 2016, the first sub-unit from the main group NCT. The group's lineup is rotational, with the members changing each promotional cycle. The members are all part of the pre-debut group SMROOKIES created by S.M. Entertainment. Taeyong, Ten, Jaehyun, and Mark were introduced in 2013, while Taeil and Doyoung were introduced in 2015. The first six members to debut with NCT U were Taeil, Taeyong, Doyoung, Ten, Jaehyun and Mark. Their first single "일곱 번째 감각 (The 7th Sense)" was released on April 8, 2016. Their second single "WITHOUT YOU" was released on April 10, with the Korean version recorded by Taeil, Doyoung, and Jaehyun, and Chinese version recorded by Taeil, Kun, Doyoung and Jaehyun. In mid-January 2018, NCT was reported to be unveil a "large-scale project" for the year, titled NCT 2018. On January 30, 2018, S.M. Entertainment released a video titled "NCT 2018 Yearbook #1," which featured existing members and introduced new members Kun, Lucas, and Jungwoo. All NCT sub-units were revealed to be participating in the project. The first and single for the project were revealed to be saved for NCT U. The second member line-up included Taeyong, Doyoung, Jaehyun, Mark, Winwin, Jungwoo and Lucas. NCT U's third single "BOSS" was released on February 18, 2018. On February 26, NCT U as Ten and Taeyong released "Baby Don't Stop". NCT released their first full-length album, NCT 2018 Empathy, on March 14. On October 12, 2020, new members Shotaro and Sungchan debuted in NCT with NCT RESONANCE Pt. 1 - The 2nd Album, the first part of NCT's second full-length album.