It became Tohoshinki's first Japanese single to reach #1 on the Oricon Weekly sales chart in Japan, making the group the first foreign male group or boyband to top the Japanese charts and second Korean artist after BoA to do so.

According to the members, the name "Purple Line" refers to the thin rays of light on horizon when the sun sets.

The music video was shot in South Korea, the first time for a Japanese single by the group.

First, a shortened music video was released in Japan for the Japanese version of the song.

On February 4, 2008, SM Entertainment surprised fans with the release of the full music video; however, with the Korean version of the song.