Netflix's new original K-drama, "The Sound of Magic," is now dominating the streaming service, being No. 1 in many countries. But aside from the great story, it also features a set of songs that many will never forget and it includes "Knees" by IU.

Director Kim Seong expressed his gratitude toward IU for letting "The Sound of Magic" use "Knees" for free. Though he tried to pay for it to avoid copyright issues, the 28-year-old singer refused.

The filmmaker revealed his talk with the K-pop star to Celeb Media via AllKpop. He said they chose to use the song "Knees" for the series and gave credits to Lee Ji Eun, which is IU's real name, in the ending credits.

However, to do that, they had to purchase the track's copyright so that they could play "Knees" in the drama worldwide. So, he contacted IU, but she refused to be paid to his surprise.

IU said she wrote and composed the song herself, so they could freely use it. Kim Seong was so thankful, revealing they had known each other since they filmed the series "Dream High."

IU chose the song "Knees" as a representation of herself. In one of her concerts, she said that when she died, the songs she wanted to be remembered that represented her were "Heart," "Knees" and "Night Letter."

Meanwhile, "The Sound of Magic" is a new K-drama based on the webtoon of the same name by Ha Il Kwon. It started to serialize in 2010. It tells a magical story of a magician living in an abandoned theme park who disenchanted a teenager suffering from the harsh realities of life.

Flix Patrol, the online content service ranking site, revealed the new show ranked first in Netflix Popular TV Programs in 15 countries all over the world. Overall, it was the fifth most popular series.

The show dropped on May 6 in 190 countries, featuring a new form of K-drama by making it a little musical. It introduced Ri Eul (Ji Chang Wook), Yoon A Yi (Choi Seong Eun) and Na Il Deung (Hwang In Yeop).

In "The Sound of Magic," they can be seen singing and dancing, which are rare in Korean TV series. In fact, Kim Seong is said to be the first director to take this challenge of combining a drama with a musical layout.

Though Kim Seong said he didn't intend to make it a music drama, it turned out well. "The Sound of Magic" is now available to stream on Netflix.