Si☆4

 is an indie local idol group created by St. Bonapro School. It is the name for the newly reorganized St. Bonapro School. The name means "Si(ster) Stella(r stars)". Four members of St. Bonapro are also in Si☆Stella and two new girls completed the lineup. Si☆Stella officially formed shortly after St. Bonapro School broke up on November 21, 2014. They had their live debut on December 21, 2014.

Current Members

 * Kashiwa Ayana (柏 綾菜; Blue ),
 * Kashiwa Yuina (柏 結菜; Orange ),
 * Furuoka Koharu (古岡 瑚遥; Purple ),
 * Sugawara Miina (菅原 みいな; Green ),
 * Yajima Ayano (矢島 彩乃; Pink ),

Former Members

 * Mafune Nono (graduated 31st August 2015) (真船 乃暖; Yellow ) ,
 * Akai Sakura (graduated 12th June 2016) (赤井 桜; Green ) ,
 * Sakurai Rico (graduated 23rd December 2016) (櫻井 理子;  Red ) ,
 * Nakamura Yuuhi (graduated 8th July 2017) (中村 柚陽; Yellow ) ,
 * Masuda Hina (graduated 5th November 2017) (増田 陽菜; Pink ) ,
 * Kikuchi Yua (graduated 19th March 2019) (菊地 結愛; Yellow ) ,
 * Okafuji Lulu (graduated 6th September 2019) (岡藤 瑠々; Red ),

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-Present)

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.