Guardians 4, a Japanese idol project group formed by Up-Front Promotion in 2009 and associated with Hello! Project, was created to perform music for the Shugo Chara! anime series. The group consisted of Aika Mitsui from Morning Musume, Yurina Kumai and Risako Sugaya from Berryz Kobo, and Saki Nakajima from Cute. Their debut single "Omakase Guardian" was released on May 27, 2009, serving as the opening theme for Shugo Chara!! Doki. The song marked their breakthrough moment in music career, gaining significant attention due to its association with the popular anime series. Following this, Guardians 4 released several notable singles including "School Days" (September 2, 2009), which was a cover version of a previous release by Shugo Chara Egg!, "PARTY TIME" (November 18, 2009), and "Going On!" (January 20, 2010). Their final single, a double A-side release featuring "Going On!" and "ありがとう〜大きくカンシャ!〜", was released on January 20, 2010. The group's only album, しゅごキャラ! ソング♪ベスト, was released posthumously on March 10, 2010, two weeks before the group's disbandment. This compilation album featured songs by Guardians 4, as well as contributions from Shugo Chara Egg! and Buono!. Guardians 4 disbanded on March 27, 2010, following the conclusion of their activities related to the anime series. The group's music played a significant role in the soundtrack of Shugo Chara!, contributing to the cultural impact of the series and leaving a notable mark on the Hello! Project discography.