"Butter-fly" (Japanese: Butter-fly, Batafurai) is a song perfomed by Kōji Wada and is his debut song. The 8cm single CD of the same name, which also includes the song "Seven", was released under the Index Music label (now T.Y.Entertainment) on April 23, 1999.
It was the opening theme song for the TV anime series Digimon Adventure. The "Strong Version" cover and the "tri. Version" of the song, also performed by Wada, were released on April 22, 2009 and November 25, 2015 respectively, with the tri. Version cover being used as the opening theme song for the 6-part anime movie series Digimon Adventure tri. Sadly, Wada passed away on April 2, 2016, five days after the release of his last single "Seven ~tri. Version~".