Seo Sung Hyuk

In 2017, he participated in Mnet's survival show Produce 101 Season 2 but was eliminated in episode 10 and finished in 31st place. Following the show's conclusion, he debuted as a member of the project group RAINZ in October 2017 before they disbanded a year later. On June 6, 2019, Sunghyuk signed an exclusive contract with Think About Entertainment.

He released a digital single titled "Good Night, My Dear" on September 24, 2019 as a special gift to his fans. On August 11, 2021, he was introduced as the 24th contestant of the survival show Wild Idol. During the show's finale, he was revealed to have ranked 4th overall, thus making him a member of TAN.