On December 2, 2016, Lee Heeseung walked out of the Hanlim Arts High School entrance exam wearing a red padded jacket. He had just finished the test. He had no formal training in singing or dancing. He was 15 years old, and he had been dreaming of becoming a singer since age six, but had never pursued it professionally. What happened next would redirect the course of his life.1

Hong Seung Woo, Big Hit Entertainment's casting head, spotted him. "I spotted HEESEUNG leaving an arts high school entrance exam wearing a red padded jacket, but whose face is what immediately caught my eye," Hong recalled in a Weverse Magazine interview. The immediate visual impact led to a conversation. Heeseung had just been approached by 7-8 different entertainment company officials for casting—evidence that multiple agencies had recognized his potential. But Big Hit Entertainment was "the quickest who wanted to sign a contract with him," and Heeseung chose them for that reason.1

For his Big Hit audition, Heeseung sang "Woo-ah (우아해)" by Crush, the Korean R&B artist. "Although Heeseung had never had any training whatsoever, he showed clear potential during his audition," Hong explained. "You could tell HEESEUNG had a feel for singing right from the start." The instinct was there. The technique would come later. On December 2, 2016, Heeseung signed with Big Hit Entertainment and began what would become a 3 year and 1 month training period—the longest among all future ENHYPEN members.1

Heeseung's training period was defined by two opposing forces: exceptional achievement and devastating exclusion. Hong Seung Woo described him as having "the skill and the attitude to make him, in the other ENHYPEN members' words, the 'model image and paragon of a trainee,' placing him top of the trainee class every month." He trained alongside the members of TOMORROW X TOGETHER, developing his vocals, dance, and production skills. He discovered he had perfect pitch—the ability to identify two to three notes simultaneously. By October 2020, he had set a personal goal to practice vocals for one and a half to two hours every day, developing a 3-octave vocal range.1

But in March 2019, TXT debuted without him. On I-LAND, Heeseung opened up about the emotional toll: "He should have been glad to congratulate TXT on their debut, he was having a hard time, as he didn't make the final lineup for TXT despite training alongside the members." The experience of watching his friends debut while he remained behind was crushing. Yet it also became the catalyst for transformation.2

The turning point came through YEONJUN, TXT's leader. In a Weverse Magazine interview, Heeseung explained: "After I saw YEONJUN, I realized I was totally fooling myself. I felt like YEONJUN was the kid who gets perfect in every subject while I was the one who gets about 80 in one class and goes around bragging about it." The realization shattered his complacency. "I thought there was no room for feeling 'not confident' and that I needed to really up his game if I wanted to be a singer." The pain of being left behind had forced him to recalibrate his entire approach to training. When I-LAND came in 2020, Heeseung was ready.3

In Episode 1 of I-LAND, which premiered on June 26, 2020, Heeseung performed NCT U's "Boss" solo. He didn't hesitate. The majority of trainees voted him into I-LAND immediately, and he was chosen as group center for the first "Into The I-LAND" performance. But the position quickly became contentious. Some trainees—including Youngbin, K, Seon, and Ni-ki—expressed concerns about how he was running practice. Heeseung saw the fractures forming. He stepped down from the center position and gave it to Ni-ki.4

Later, he reflected: "When I said on day one that I didn't want to be the center, it was because I knew this kind of result would happen." The foresight was remarkable for someone so young, but it carried a bitterness. "I really worked even harder for my team, but I think that has rather become an arrow back at me." Still, he pushed forward. In the "Flicker" performance, Heeseung—who had placed first in the first test—won the benefit of choosing the song and selecting his teammates: Sunghoon, Jake, Jungwon, and K. Team Flicker performed in maroon suits with polished precision.4

On September 18, 2020, the I-LAND finale arrived. Heeseung earned fifth place with 1,137,323 votes, securing his debut. But another leadership question loomed: Who would be the group's leader? After 40 days of deliberation between two candidates—Heeseung and Jungwon—Heeseung called Jungwon over the night before the final decision. He told him he wanted Jungwon to be the leader instead. His reasoning was strategic and selfless: "I thought it would be better if I remained a team member and the oldest member because if the oldest member also becomes the leader, the other members might be hesitant to express their opinions clearly." He also didn't want Jungwon to experience the same pressure he had felt as a leader on I-LAND. Jungwon became leader. Heeseung became the eldest member who refused to wield his seniority as power.5

On November 30, 2020, ENHYPEN debuted with "Border: Day One," selling 280,873 copies in the first week—the bestselling K-pop debut of 2020. Heeseung took his position as main vocalist and center, delivering vocal performances that showcased the three-octave range and perfect pitch he had honed over three years. But his ambitions extended beyond performance. He wanted to create.6

In 2024, Heeseung became the first ENHYPEN member to receive producer credit. The song was "Highway 1009," a fan-dedicated track from the group's second studio album "Romance: Untold." According to Weverse Magazine, it took approximately three hours to make the demo with a friend. All seven members—Heeseung, Jake, Jay, Jungwon, Ni-ki, Sunghoon, and Sunoo—co-wrote the lyrics. Heeseung earned his first KOMCA (Korea Music Copyright Association) credit as composer, lyricist, and producer.7

The achievement was a continuation of his artistic philosophy. In a 2023 Weverse Magazine interview titled "I think that's what a pro would do: show people exactly what they want to show them," Heeseung explained that he thinks about ENGENE whenever he records vocals, considering what the song will feel like to sing live later. "Performing live in front of many ENGENE has led to me looking cooler and more effortless on stage," he said. By 2024, in another Weverse Magazine interview, he described his strength as "doing things without anyone having to tell him to—trying out creative, new things on his own." He considered himself "pretty well-rounded."8

On May 30, 2022, Heeseung posted a cover of Justin Bieber's "Off My Face" to ENHYPEN's official YouTube channel. He performed against floor-to-ceiling windows overlooking a cityscape, his voice smooth and effortless. "'Off My Face' is a song I often enjoy listening to by an artist whom I highly respect," he explained. In a Weverse Magazine interview, he wanted "a space with a laid-back atmosphere so people could easily focus on his vocals." Both Billboard and Rolling Stone featured the cover, recognizing his vocal interpretation and emotional delivery.9

On October 12, 2024, at Music Bank in Madrid, Heeseung performed The Weeknd's "Can't Feel My Face" in front of 35,000 K-pop fans. Dressed in a leather jacket, he described it as "almost like a freestyle performance" and said "it was more fun because I didn't really practice before going." The performance left the crowd speechless from his intensity and magnetism. He left the extended stage to get closer to fans at the barriers, embodying the dream he had articulated: "Performing solo onstage was part of my dream."10

But the defining performance came at Coachella Valley Music and Arts Festival on April 11-13 and April 18-20, 2025. ENHYPEN became the K-pop boy group with the shortest time between debut and performing at the festival. According to Weverse Magazine, during rehearsals on the outskirts of Los Angeles, members "practiced at full volume, adjusting their vocal technique and projection, led by HEESEUNG." The 45-minute set opened with "Blockbuster" followed by a rearranged "Blessed-Cursed" and "Future Perfect (Pass the MIC)." Afterward, Heeseung called their Coachella performance "the most gratifying stage I've done in my career."11

The boy in the red padded jacket who was street-cast outside Hanlim Arts High School had stood on the world's most famous music festival stage, leading his group's vocal preparations, performing with precision and confidence. The training period had been long. The exclusion from TXT had been painful. The I-LAND center position had crumbled beneath him. The leader role had been declined. But through it all, Heeseung had become what Hong Seung Woo saw on that December day in 2016: someone with a feel for singing right from the start—and the relentless drive to turn potential into mastery.