Under17 (stylized as UNDER17) was a Japanese musical duo formed in 2001 by Haruko Momoi and Masaya Koike.
On 27 September 2004, it was announced that Under17 would break up after their national tour, with Momoi and Koike going separate ways due to creative differences.
[3] Momoi officially embarked on a solo career and Koike formed the band MOSAIC.WAV.
The band reunited for one song on 31 August 2008 during the Animelo Summer Live, performing "Tenbatsu!
[4] Momoi and Koike briefly reunited again in March 2020 to perform at the event Susume Moe Denpa Shōnen!!