This song is based on a Korean folklore that brings about a traditional celebration known as the Chilseok or Qixi Festival (七夕 “The Night of Sevens”).

There are multiple versions of this folklore. One of it is a celestial princes called Jik Nyeo (a woman who weaves cloth) met a cow-herder named Gyun Woo. They fell in love when Jik Nyeo went to earth one flowery spring day and they promised to get married.
However Jik Nyeo’s father – the king of heaven – was furious for the fact that her daughter fell in love with an earthling. He punished them by separating them; Gyun Woo to live in the faraway lands in the east and Jik Nyeo, faraway lands in the west, across the Milky Way.
Devastated, Jik Nyeo begged her father so they could still meet each other. In return the king of heaven let them see each other once a year across the Milky Way on ‘Chil Seok’, the 7th day of the 7th lunar month.