A scene from the TV series "Descendants of the Sun," starring Song Joong-ki (left) and Song Hye-kyo (KBS)

Behind the phenomenal success of the TV drama series “Descendants of the Sun,” which recorded nearly 40 percent viewership ratings, was the soundtrack that enhanced the completeness of the drama.

Aired in 2016 on KBS, "Descendants of the Sun" depicts the love story between Army Captin Yoo Si-jin (Song Joong-ki) and Kang Mo-yeon (Song Hye-kyo), a medical doctor, in the fictional land of Uruk. The second lead pair, First Lieutenant and Army Doctor Yoon Myung-joo (Kim Ji-won) and Master Sergeant Seo Dae-young (Jin Goo), also garnered a significant fan following. Skillfully weaving romance with the heroism of soldiers and doctors, the series deeply resonated with K-drama fans around the world.

Each character is given a theme song that deepens the emotional depth of the scenes.

Yoon Mi-rae, the popular female rapper and singer, crooned, "Even if everything changes, I won't change. You're my love, and I'm yours. Even if you pass by again, I'll be here for you."

The track "Always" was first used in the latter part of Episode 1. Yoo develops feelings for Kang, but abruptly leaves on a secret mission before he can ask her out. Just before departing on a helicopter, the scene where they promise to go on a date upon his return is accompanied by "Always," adding poignancy to the story of a man who has to prioritize duty over love and a woman who falls in love with him.

Gummy's "You Are My Everything" was used in the final scene of Episode 4, as the two kiss. Kang discovers that Yoo had received disciplinary action for disobeying orders while helping her perform surgery on a VIP patient. She begins to understand Yoo's position as a soldier and her feelings become complicated.

A scene from the TV series "Descendants of the Sun," starring Jin Goo (left) and Kim Ji-won (KBS)

The second lead couple, Yoon and Seo, break up in the face of strong disapproval by Yoon's father. Yoon pushes away Seo, who is about to quit his military career to gain his father's approval, knowing how much he cherishes his honor as a soldier.

Duo Davichi's "This Love" conveys the story of lovers who long for each other despite breaking up for each other's sake: "If I could turn back time, would memories also be erased? I’ve said things that can't be done, because I regretted making you suffer and live with tears."

Repeating the lines, “But you see, I cannot live without you. Only the time full of you passes by," the song signifies that the two will eventually seek each other again.

"Once Again," sung by Korean American rapper Mad Clown and ballad singer Kim Na-young, was also much loved. A blend of hip-hop beats and piano melodies, the song features lyrics by Mad Clown that portray Seo's feelings as he pushes away Yoon. "No matter how much I think, the answer is you, but I'm writing the wrong answer in my heart. Even if I push you away, you remain."

In the latter part of the drama, Yoo and Seo go missing while carrying out a dangerous mission, but miraculously return to their lovers.

When Yoo appears over the sand dunes and hugs Kang, "With You" played in the background, ballad singer Lyn's tearful voice adding to the dramatic moment of their reunion.

In the scene where Seo returns to Yoon, "By My Side" by SG Wannabe is played. The lyrics convey Seo's sentiment: “Not being able to see you is the scariest thing in the world to me, even more than death itself.”

The lyrics echo Yoon's line from the previous episode: "The scariest thing in the world is not being able to see the one I love.”

Sweet dating scenes also contributed to the drama's popularity.

K.will's "Talk Love," a bright song featuring whistling, rhythmic guitar and lively piano melodies, was used in scenes where the two couples enjoy brief moments of peace. The lyrics express the hesitation of a man who wants to confess his love: "Tell her, what are you doing? All the love that comes to me is in the name of you."

Accompanying several scenes where Yoo and Kang develop feelings for each other was "Everytime," sung by Exo's Chen and singer-songwriter Punch. The song features a refreshing melody and orchestral sounds.

A scene from the TV series "Descendants of the Sun," starring Song Hye-kyo (KBS)