"But" / "Aishō" is Koda Kumi's 35th single and was released on March 14, 2007. It was her first single of 2007. The single was a time-limited purchase, only being sold from March 2007 to May 2007. "Aishō(愛証?)", meaning "Love Proof", is a love ballad. "But" is also the theme song for the Japanese edition of the movie, Step Up. Aishō was used as the drama Ai no Rukeichi's theme song.
There was also an analog version of But, set for release the week after this single's.
"But" is certified triple platinum as a ringtone and platinum as a digital download to cellphones by the RIAJ.(ringtone): 3× Platinum(cellphone): Platinum "Aishō" is certified platinum for downloads, and the single is certified gold for 100,000 copies shipped to stores.
The PV for But consisted of Kumi, at the beginning, sleeping in a large chair dressed in frivolous clothes, revealed to be chained to the ceiling by a pulley. She attempts to break out of the chain, and once she does, she runs around the room in a girlish manner. The mood changes from playful to more provocative as she descends an elevator into a new room. This room is full of men dressed in women clothing (two men) dressed in bellhop clothing, bowing there are hints of homosexuality involved between the men in a small portion of the music video. The video's scenes continue to alternate between the rooms as the song continues, and at the end, Kumi wakes up in the green room. Everything seems to have been a dream.
The PV for Aishō is set in Feudal-era Japan, and in a large shiro. Kumi at the beginning is walking through a twilit hall in a shoulder-bare kimono, as she enters another room and proceeds to remove her upper layer of clothing. There are cut-scenes of her in a doorway against a moonlit night, and then her, ravaged on a bed. After this, there are scenes of her reclining in another room, smoking. There are also animated scenes of a bird flying through the night, as the video ends by going through the other rooms.