Si☆4

 (read as Si Four), formerly a sub-unit of Si☆Stella, was an indie local idol group created by BONAMII Inc. (or Bonamii Model Production). The group was originally formed in July 2013 as St. BONAPRO SCHOOL (聖☆ボナプロ学園). They disbanded in November 2014 and reformed as Si☆Stella the next month. The name means "Si(ster) Stella(r stars)". They made their live debut on December 21, 2014.

In August 2018, Si☆4 was created as a sub-unit. Si☆Stella disbanded in December 2019, and Si☆4 continued on their own. Si☆4 disbanded on April 29, 2022.

Si☆4 Members

 * Kashiwa Ayana (柏綾菜; ) (Joined December 2014)
 * Kashiwa Yuina (柏結菜; ) (Joined December 2014)
 * Furuoka Koharu (古岡瑚遥; ) (Joined February 2016)
 * Sugawara Miina (菅原みいな; ) (Joined August 2018)

Si☆Stella
In addition to the above girls, Si☆Stella consisted of:
 * Sakurai Rico (櫻井理子; ) (Founding member, graduated December 23, 2016)
 * Mafune Nono (真船乃暖; ) (Founding member, graduated August 31, 2015)
 * Akai Sakura (赤井桜; ) (Joined September 2014, graduated June 12, 2016)
 * Nakamura Yuuhi (中村柚陽; ) (Joined October 2015, graduated July 8, 2017)
 * Masuda Hina (増田陽菜; ) (Joined December 2014, graduated November 5, 2017)
 * Kikuchi Yua (菊地結愛; ) (Graduated March 19, 2019)
 * Okafuji Lulu (岡藤瑠々; ) (Graduated September 6, 2019)
 * Yajima Ayano (矢島彩乃; ) (Joined June 2019, left December 2019)

Sub-Units

 * BONAMETAL (Mafune Nono, Akai Sakura, Sakurai Rico, Masuda Hina, Kashiwa Ayana and Kashiwa Yuina) (2014-2018)
 * Si☆4 (Kashiwa Ayana, Kashiwa Yuina, Furuoka Koharu and Sugawara Miina) (2018-2022)

Live Albums

 * 1) [2016] Si☆Stella Live Album -2016-
 * 2) [2017] Si☆Stella Live 2016/12/23 -Rico☆Stella The Last-
 * 3) [2018] Si☆Stella Live Album -2018-

Mini Albums

 * 1) [2015.08.15] (pre-released digital download on 2015.07.17) Si☆Stelland
 * 2) [2017] Si☆Stella La Land

Single

 * 1) [2018.04.30] Natsu Koi☆HANABI

Album

 * 1) [2020] LIVE ALBUM -2020-

Mini Album

 * 1) [2019.03.24] Si☆4 U

Single

 * 1) [2019.07.07] Nijiiro☆Mirai

Digital Single

 * 1) [2018.11.15] Futari☆Destiny

Trivia

 * They were being promoted as the youngest idol group when the group first formed on December 21, 2014.
 * The eldest Si☆Stella members Kashiwa Ayana and Kashiwa Yuina are fraternal twins.