"Mysterious" is an original Luo Tianyi song. The lyrics have no specific meaning as it is meant to be a song for people to dance to, thus leaving it open for interpretation.
The full version of the song was featured in the album, Dual Sight. It should be noted that it has been uploaded on NicoNico by the official VOCALOID store channel instead of Hachioji-P or wakaura's channels.
Flexin's MMD PV was used to promote the Dual Sight album. This version exceeded 100,000 views on bilibili.