Si☆4

 (read as Si Four) 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)

Former Members
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-groups

 * 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)

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.