all at once (オールアットワンス) are a J-pop duo formed in 2018. The duo was formed when its member, Itsuki, asked Narito to be his duo member when they had to perform at the event sponsored by the music school in Tokyo, where they both graduated. The duo was later discovered by the Japanese record label Being and made a contract with the company. In April 2020, they released the debut single "12cm", produced by Seiji Kameda.

Their debut extended play, Just Believe You (2020) reached number 20 on the Oricon Daily Albums chart. The extended play consists of the previously released singles: "12cm", "Hoshiai", and "Just Believe You". The latter two have served as the theme songs to the Japanese animated television series, Case Closed.