"Swallowtail Butterfly (Ai no Uta)" (あいのうた, Suwarōteiru Batafurai Ai no Uta, "Love Song") is a song by Chara, released under the name Yen Town Band. It was the lead single from Montage, a concept album released for the Shunji Iwai film Swallowtail Butterfly that also starred Chara. This song was used as the theme song for the film. The single debuted at #31 on Oricon's singles charts. Two months later, after the release of the film and album, the single managed to reach #1. The song was written by Takeshi Kobayashi, in collaboration with Chara and film director Shunji Iwai.