I have had a dream about an anime that is almost close to your idea.
However, the key difference is that it is a mahou shoujo anime. A shoutout to magical girls of old like Creamy Mami and Magical Emi. Five girls, all aspiring musicians, about 12 y/o. The leader is a vocalist, absolute fan of Freddie Mercury. The second is the guitarist, whose inspirations are Jimi Hendrix, Yngwie Malmsteen and Joe Satriani. The third is the bassist, her hero being
James Entwistle. The third is a half-scandinavian girl, absolute fan of
Hellhammer, as you can guess she is the drummer. The last one is a keyboardist, her role model is
Jordan Rudess, but she can oassionally swap her keyboard for a chapman stick.
The mascott would have been a suspicious cat thing that speak with a baritone voice a la Jouji Nakata and his goal is to actually save his universe with the energy coming from the power of rock, and its fans. The arcs would have mostly been, The girls.. vs Doom Metal, ... vs Thrash Metal, .... vs Power Metal, ... vs Symphonic Metal, ... vs Punk, ....vs Psychodelic (style like The Doors or Black Angels), ...vs Black Metal, ....vs Progressive.
So yeah, it would have been mostly educational about the different genres, and show metal/rock bands battles. And the girls would have hard time to manage their normal lives (school, love interests, parents, etc..) and their lives as magical girls metal band. They would be that kind of overnight sensation and eventually fade out as their time in middle school end and graduate to reach high school. It end with them turning back to normal, but even emotionally, mentally and artistically grown. And flash years later when they enters university and reunites again, this time to make their own band. Without the help of the magical mascot.