NCT U’s debut and the start of the NCT brand was presented through “일곱 번째 감각 (The 7th Sense),” an experimental combination of R&B, trap, and hip-hop that shows the groups' individualism and flexibility as performers.

Even though the name “7th Sense” was first linked to NCT on February 1 with the ensemble’s third teaser, NCT U’s debut wasn’t officially announced until April 4, through SM Entertainment’s official Twitter account, that first revealed teaser pictures for members Jaehyun and Mark and reported that they would be debuting NCT U, the first unit of NCT, with two digital singles—including EDM rock song “WITHOUT YOU.”

NCT U made their broadcast debut through a V-App program hosted by Kim Hee Chul on April 9 and 10. Their first live performance was in China at the Top Chinese Music Awards event held on April 9. The group made their official debut stage in Korea at KBS Music Bank on April 15.