Being Taeil’s first solo delivery, “단 한 사람 (Because Of You)” is a ballad that sings about eternal love and takes part in the original soundtrack of the period drama, 장사의 신 – 객주 2015 (The Merchant: Gaekju 2015).

The song credits Taeil as a member of SMROOKIES, SM Entertainment’s pre-debut training team, since it was released three months before Taeil was announced as a member of NCT’s first sub-unit, NCT U. “단 한 사람 (Because Of You)” is the only official pre-debut release by an SM Entertainment trainee.

On February 1, 2016, the song achieved the tenth place on China’s Baidu King Chart. Later on, on April 19, the Korean ballad escalated to the first place.