It is a song written and composed by CNBLUE’s Zheng Yonghe himself

There are two versions. One version is called "Pingyu Song", which is a duet version between Zheng Yong and Seohyun

Another version is called "For the Lovers Who Fall in Love for the First Time" Yonghwa's solo version is the background music of Yonghwa and Seohyun writing on the ground

The lyrics of the two versions are different and both are very nice!