X21, also known as Next Generation Unit X21 (次世代ユニットX21), was a Japanese idol group formed in 2013 by Oscar Promotion.

Members of the group were the finalists of the 13th Japan Bishojo Contest in August 2012. Yoshimoto Miyu and Ozawa Nanaka were the winners of the beauty contest.

The “X” in the group’s name stands for “unknown”, “future” and “power that can not be predicted”. It indicates that they are the next generation idol unit and that their potential is unpredictable.

Their variety show Go! Oscar! X21 (Go!オスカル!X21) has aired on TV Asahi (テレビ朝日)  since April 2013. 

Members

1st Generation:

Yoshimoto Miyu (吉本実憂) - Leader
Ozawa Nanaka (小澤奈々花) - Sub-Leader
Izumikawa Miho (泉川実穂)
Yamasaki Saaya (山﨑紗彩)
Matsuda Rina (松田莉奈)
Moriya Sakura (籠谷さくら)
Tanaka Shuri (田中珠里)
Nagao Mami (長尾真実)
Igashira Manami (井頭愛海)
Osaki Ichika (尾碕真花)
Shiratori Hasumi (白鳥羽純)
Kaminaguchi Honoka (上水口萌乃香)
Yamaki Koharu (山木コハル)
Onishi Aguri (大西亜玖璃)
Suenaga Mai (末永真唯)
Ozawa Nanaka (小澤奈々花) 

2nd Generation:

Takamura Yuka (髙村優香)
Kadogaki Hikaru (門垣ひかる)
Kawaguchi Yurina (川口ゆりな)
Iijima Mika (飯島未賀)
Inuzuka Shiori (犬塚しおり)
Nakazato Megumu (中里 萌)

Former members:

Nishikawa Misaki (西川美咲) 
Wakayama Ayano (若山あやの) 
Sera Misaki (瀬羅美咲) 
Sagawa Miyu (佐川実優) 
Hosoi Yurika (細井友里加) 
Takahashi Runa (高橋るな)