One idea could be a singing competition where the groups from both 'Pitch Perfect' and 'Glee' participate. They could start off as rivals, but then gradually learn from each other's styles. For example, the Barden Bellas could teach the New Directions some of their a cappella arrangements, while the New Directions could introduce more pop and show - tune elements to the Bellas.
Maybe there's a story where a character from 'Glee' transfers to the university in 'Pitch Perfect'. This character could try to join the Barden Bellas and cause some drama within the group as they have different ideas about music and performance. At the same time, they could also introduce some of the Glee - style group numbers to the Bellas, leading to a new and exciting sound for the group.
A crossover with 'High School Musical' would also be cool. Picture the Pitch Perfect girls and guys going to the same school as the High School Musical characters. There could be a big musical showdown where the two groups have to combine their talents. The Pitch Perfect crew's edgy acapella style might clash and then blend with the more traditional musical theater style of High School Musical, leading to an amazing performance.
One idea could be a prequel focusing on how the Bellas formed in the first place. Maybe explore the early relationships between the members like Aubrey and Chloe.
One plot idea could be that the Barden Bellas somehow get caught up in a supernatural hunt. Maybe they're performing at a haunted location and strange things start to happen. The girls then team up with the Winchesters to figure out what's going on and stop the evil entity.
Rachel Berry from 'Glee' would be a key character. She is so ambitious and has a strong vision for music. In a crossover, she could clash with Aubrey from the Barden Bellas over leadership and musical direction. This conflict could drive the story forward as they both try to prove their way of doing things is the best.
One idea could be that the OC is a new student at Barden University and has an amazing, unique vocal talent that catches Donald's attention during auditions for the a cappella groups. Maybe the OC has a secret past related to music that gradually unfolds throughout the story, and Donald helps the OC overcome some insecurities related to it.
One idea could be a singing competition between the Glee club and the students from Victorious. They could meet at a national music event and initially be rivals, but then start to collaborate and learn from each other's styles. For example, the Glee club could teach the Victorious crew about more traditional musical theater numbers, while the Victorious students could introduce the Glee club to more modern pop and hip - hop influenced performances.
One plot idea could be that the Shadowhunters need to find a way to defeat a powerful demon that can only be weakened by a special type of music. So they seek out the Glee club. The Glee club members are hesitant at first but then realize the importance of their role. Another idea is that a spell gone wrong in the Shadowhunters' world sends some of their key characters to the Glee club's world. There, they have to adapt to high school life while also trying to find a way back. And the Glee club helps them blend in and in return, they learn about the Shadow World.
A plot could involve a character from Glee accidentally stumbling into the Starkid universe. For example, Rachel Berry could find herself in the middle of a Starkid rehearsal. She might initially be confused but then realizes she can learn a lot from their unique style of performing. This could lead to a series of comical and heartwarming interactions as she tries to fit in and contribute to their shows.
One idea could be exploring the backstories of the characters in more detail. For example, what made Fat Amy so confident? Another could be creating a new a cappella group that challenges the Barden Bellas. Maybe they have a unique style or set of members.
One idea could be that some of the Glee characters visit Mystic Falls for a singing competition. While there, they get caught up in the vampire drama. Maybe a vampire takes a liking to Rachel's voice and wants to turn her into a vampire so she can sing forever. Another plot could involve the vampires using the Glee club as a cover to hunt during their events.