Love Letter

is a song by Japanese duo Yoasobi from their second extended play, The Book 2 (2021). It was released on August 9, 2021, through Sony Music Entertainment Japan. The song was written by Ayase and based on Hatsune's letter Ongaku-san e, which won the Letter Song Project, a collaboration with radio show Sunday's Post. "Loveletter" peaked at number three on the Oricon Combined Singles Chart, and number four on the Billboard Japan Hot 100.