蜉蝣 (kagerou) was a Japanese rock band which was first formed in September 1999 by 大佑 and then-bassist MASAYA. ユアナ joined as the guitarist a month or so later, and the band performed their first live together at CYBER on February 13, 2000. On April 4, their first Maxi Single, titled Biological slicer, was released, and in the following May, 静海 joined the band. With this lineup, 蜉蝣 performed at many lives around the country. However, shortly after the band played at Meguro Live Station on October 11, MASAYA left the band, thus causing 蜉蝣 to go on a temporary hiatus.