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Also known asPoly-Phonic
OriginTokyo, Japan
Years active2001–2004
Past members

Under17 (stylized as UNDER17) was a Japanese musical duo formed in 2001 by Haruko Momoi and Masaya Koike.[1] The group was known for producing music known colloquially as "moe songs",[2] providing theme and insert songs to series such as Tenbatsu! Angel Rabbie, Popotan, and DearS.


Some of the anime series where Under17 songs have been featured are Mouse, Popotan, Tenbatsu! Angel Rabbie, Hourglass of Summer, DearS, and Kujibiki Unbalance.[2] This group has released several adult videogames' opening songs. 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. Their final concert was held on 20 November 2004 at the Yokohama Blitz.[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! Angel Rabbie" with the members of MOSAIC.WAV.[4]

Momoi and Koike briefly reunited again in March 2020 to perform at the event Susume Moe Denpa Shōnen!! Daifukkatsusai 2020!!: Sugisarishi Moe o Motomete.[5][6]


  • Haruko Momoi (桃井はるこ) (vocals)
  • Masaya Koike (小池雅也) (guitar)


Compilation albums[edit]

Title Year Details Peak chart positions Sales
Under17 Best Album 1: Bishōjo Game Song ni Ai o! (UNDER17 BEST ALBUM1 美少女ゲームソングに愛を!) 2003
  • Released: 3 December 2003
  • Label: Lantis
  • Formats: CD
Under17 Best Album 2: Moe Song o Kiwameruzo! (UNDER17 BEST ALBUM2 萌えソングをきわめるゾ!) 2004
  • Released: 21 January 2004
  • Label: Lantis
  • Formats: CD
Under17 Best Album 3: Soshite Densetsu e... (UNDER17 BEST ALBUM3 そして伝説へ…)
  • Released: 22 December 2004
  • Label: Lantis
  • Formats: CD
"—" denotes releases that did not chart or were not released in that region.


Title Year Peak position Sales
"Mouse Chu Mouse" (マウス Chu マウス) 2003 68
"Popotan E.P." (ぽぽたんe.p.)
(with Funta)
"Love Slave" (ラブスレイブ) 2004 55
"Kujibiki Unbalance" (くじびきアンバランス) 68
"—" denotes releases that did not chart or were not released in that region.


  1. ^ "FanimeCon 2009 Announces Halko Momoi (Musician, Songwriter, & Seiyū) as a Guest of Honor". Anime News Network. 14 May 2009. Retrieved 22 May 2009.
  2. ^ a b "RJP-Pro Anouncements [sic]". Anime News Network. 8 June 2004. Retrieved 22 May 2009.
  3. ^ "アニメ". Exciteエキサイト (in Japanese). 23 October 2005. Archived from the original on 31 March 2007. Retrieved 1 October 2020.
  4. ^ "MOSAIC.WAV & UNDER17 Tenbatsu! Angel Rabbie (Live)". 29 July 2009. Archived from the original on 26 August 2014. Retrieved 21 August 2014.
  5. ^ "桃井はるこ×小池雅也のUNDER17が15年半ぶり復活、でんぱ組.incらと競演" [Haruko Momoi and Masaya Koike return as Under17 after 15.5 years, a recital contest with Dempagumi.inc]. Natalie (in Japanese). 1 January 2020. Retrieved 5 October 2020.
  6. ^ "16年ぶり復活…伝説の萌えソングユニット「UNDER17」がオタク文化に残した功績 桃井はるこ【インタビュー】" [(Interview) Haruko Momoi: a return after 16 years... the legendary moe song unit Under17, an achievement remaining from the otaku culture]. Anime! Anime! (in Japanese). 13 March 2020. Retrieved 5 October 2020.
  7. ^ Peak chart positions on the Oricon Weekly Albums Chart:
  8. ^ Peak chart positions on the Oricon Weekly Singles Chart: