Under17 (アンダーセブンティーン、アンセブ) was a popular Japanese duo, which included Haruko Momoi and Masaya Koike, that wrote and performed many moe songs that are featured in anime and video games. The lead singer, Haruko Momoi, is well known for her unique vocals and catchy lyrics. Some of the anime series where Under17 songs have been featured are DearS, Kujibiki Unbalance, Tenbatsu! Angel Rabbie, Mouse, and Popotan. This group has released several adult videogames' opening songs. On September 27, 2004, it was announced that Under17 would break up, with Momoi and Koike going separate ways due to creative differences.

The band reunited for one song on August 31, 2008 during the Animelo Summer Live. They performed 「天罰！エンジェルラビィ」 (Tenbatsu! Angel Rabbie) with the help of MOSAIC.WAV members.