Another plot could be that Summer faces some kind of personal attack outside of the band that makes her question her place in the School of Rock world. For example, she might be bullied by other music students. The fanfiction could detail how she copes with this hurt, and how her friends in the band support her and help her regain her confidence.
Perhaps Summer gets hurt in a rehearsal accident. For example, some equipment malfunctions and she gets a minor injury. This could lead to a story where the kids in the School of Rock learn about safety measures in a more serious way. They might have to postpone their shows and face the disappointment of their fans. Meanwhile, Summer could be feeling frustrated and left out, but her friends visit her often and they come up with creative ways to keep her involved, like having her write new lyrics from her hospital bed.
One idea could be a time - travel plot where a fan somehow gets transported into the 5 Seconds of Summer's school days. They could interact with the band members as they were before fame, and maybe even influence their musical journey.
It could be that Summer is kidnapped by a group of thieves who mistake her for someone else. They think she has a valuable music manuscript that's actually in the possession of another person. While kidnapped, Summer tries to convince them of their mistake. The School of Rock crew figures out she's been taken and teams up with the police. They use their knowledge of the music scene and the places Summer likes to go to help the police find her.
It could be a rival music group. They might be jealous of the success of Summer's band and try to undermine them. For instance, they could spread false rumors about Summer which cause her emotional pain.
Well, one possibility could be that Summer and Freddy have a moment during a big school concert. Maybe they share a kiss after a really amazing performance where they both realize their feelings for each other. It could start with some tension between them during rehearsals, like Freddy being a bit jealous when Summer gets more attention from the new music teacher at first.
The summer dragon could be the key to saving a kingdom that is suffering from an eternal summer. A group of adventurers sets out to find the dragon and convince it to use its power to restore the normal cycle of seasons. Along their journey, they face many challenges like treacherous terrains and other dangerous magical beasts.
One idea could be a time - traveling adventure where Summer and Morty end up in a parallel dimension where their roles are reversed. Morty is the confident, popular one and Summer is the nervous sidekick for a change.
The other characters would be very concerned. Dewey, the teacher, would probably immediately rush to her side and make sure she gets proper medical attention. Zack might be in shock at first, but then he would step up and try to take on some of Summer's responsibilities in the band, like leading the rehearsals. Freddy would be constantly checking on her, bringing her little gifts to cheer her up. And Tomika would be the one to comfort Summer emotionally, listening to her fears and frustrations about getting hurt and being unable to perform for a while.
A plot could revolve around them having a child. Rock would be the more nurturing one, while Revy would be overprotective. They could have different views on how to raise the child, like Rock wanting a more peaceful upbringing and Revy wanting to teach the child self - defense from a young age. It would lead to some interesting family dynamics and character growth for both of them.
One plot idea could be a female rock fan who discovers that Ben 10 has a secret love for rock music too. They meet at a concert and team up to save the day when an alien threat targets the concert venue. Another could be a female rock star who gets her Omnitrix - like powers and teams up with Ben 10 to battle music - hating aliens. A third idea is that a female rock fan is transported into the Ben 10 universe and uses her knowledge of rock music to communicate with some alien species that are attracted to the energy of rock music.