NCT U is the first sub-unit of NCT. They debuted with two singles that were released on April 9 and 10, 2016. Their name stands for 'Neo Culture Technology U'.
2016: Debut with "The 7th Sense" and "Without You"
On April 4, NCT U was announced with pictures announcing members Mark and Jaehyun, later adding members Taeil, Taeyong, Doyoung, and Ten. NCT U was described as the main group of NCT. It was announced that there will be two NCT U groups, each having different member organization. On April 9, they released the song “The 7th Sense” and "Without You" as digital singles, Jaehyun, Mark, Ten, Taeyong, and Doyoung participated in producing “The 7th Sense” which is described as having a hip-hop groove with a heavy base sound. As for “Without You,” members Taeil, Jaehyun, and Doyoung worked to create the dance EDM song. The group made their debut on music program Music Bank four days later.
2018: "Timeless" and NCT 2018
The single "Timeless" consisted of the "Without You" members: Taeil, Doyoung, and Jaehyun. The NCT 2018 Empathy album then gave new NCT U songs, as well as new members, such as "Boss," "Yestoday," and "Baby Don't Stop." The "Boss" lineup consisted of Taeyong, Doyoung, Jaehyun, Winwin, Jungwoo, Lucas, and Mark. Meanwhile, the "Baby Don't Stop" lineup consists of Taeyong and Ten. The "Yestoday" lineup consisted of Taeyong, Doyoung, Lucas, and Mark.