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 ), July 20, 2005
 * Kashiwa Yuina (柏結菜; Orange ), July 20, 2005
 * Furuoka Koharu (古岡瑚遥; Purple ), November 24, 2005
 * Sugawara Miina (菅原みいな; Green ), June 8, 2006
 * Yajima Ayano (矢島彩乃; Pink ), September 9, 2010

Former Members

 * Mafune Nono (graduated 31st August 2015) (真船乃暖; Purple ), July 8, 2004
 * Akai Sakura (graduated 12th June 2016) (赤井桜; Green ), November 20, 2004
 * Sakurai Rico (graduated 23rd December 2016) (櫻井理子;  Red ) , May 3, 2002
 * Nakamura Yuuhi (graduated 8th July 2017) (中村柚陽; Yellow ), October 28, 2005
 * Masuda Hina (graduated 5th November 2017) (増田陽菜; Pink ), December 10, 2008
 * Kikuchi Yua (graduated 19th March 2019) (菊地結愛; Yellow ), November 5, 2009
 * Okafuji Lulu (graduated 6th September 2019) (岡藤瑠々; Red ), August 18, 2011

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.