It's "We've Been in Love for 6 Years" by Twins
Since the Twins officially formed an army in 2001, six glorious years have passed, and 50 selected songs have been released on the 3CD "We've Been in Love for 6 Years" Old songs to thank all fans for their unwavering support over the years! In order to commemorate the sixth anniversary of their debut, Twins specially created the theme song "We have been in love for 6 years". There are also four new songs on the disc: "Floating Swallow", "Little Love", "Red Dangdang Flying Kiss" specially sung with Grasshopper Crossover and Twins The theme song of the upcoming Chinese New Year film "Gemini Thieves" is "Two in the World".
The DVD contains two new song MVs: "Little Love" and "Red Dangdang Flying Kiss", as well as the behind-the-scenes of the MV shooting with Grasshopper.