"Butter-Fly" is the debut single by Japanese vocalist Kōji Wada. It is best known as the opening theme song to the Digimon Adventure anime, debuting on April 23, 1999, as well as the closing theme to the associated film of the same name, originally released on March 10, 1999. To commemorate the 10th anniversary of the Digimon franchise as well as the 10th anniversary of the release of his initial single, Wada released a "Strong Version" re-release on April 22, 2009. The song has also been covered by Masaaki Endoh in his album Enson, and is a recurring feature of the Kumikyoku Nico Nico Douga anime theme mashup songs. Another version of the song was performed by Wada for the anime film series Digimon Adventure tri, celebrating the 15 years of the original series, and released a few months before he died on April 2016.