Imagine Echo being sent on a secret mission by the Rebels to infiltrate an Imperial base. Since he was a clone, he can use some of his old military protocols to get inundetected. Once inside, he discovers a new Imperial weapon project. He then has to work with the Rebels outside the base to figure out a way to destroy the project before it becomes a major threat to the Rebels and the galaxy at large.
A fanfiction could revolve around Echo's memories. He has flashbacks to his time in the Clone Wars that end up providing valuable insights for the Rebels. For example, he remembers a weakness in a type of Imperial droid that the Rebels are currently facing. This not only helps them in battle but also makes the Rebels see Echo as a valuable asset.
A great idea for an Echo x Star Wars Rebels crossover fanfiction would be that Echo has some sort of encrypted data in his cybernetic enhancements that could be crucial for the Rebels. The Rebels have to figure out a way to access it without harming Echo. This could lead to a lot of character - development moments as they get to know Echo and his past better, and Echo gets to adapt to the Rebels' way of doing things.
One common theme is Echo's struggle with his past as a clone trooper. Many fanfictions explore how his experiences in the Clone Wars and his time as a prisoner of the Separatists affect him in the Rebels era.
One idea could be that Master Chief somehow gets transported to the Star Wars Rebels universe. He could team up with the Ghost crew. His advanced combat skills and Spartan armor would be a huge asset against the Empire. Maybe he'd share his knowledge of advanced weaponry with the rebels.
One idea could be a crossover with the original Star Wars trilogy characters. For example, having Luke Skywalker meet the Rebels crew and learn from their guerilla warfare tactics against the Empire. It would be exciting to see how their different fighting styles blend and how they interact with each other.
One plot idea could be that a character from Clone Wars gets accidentally sent to the time period of Rebels. For example, Ahsoka Tano could end up in the middle of a battle between the Rebels and the Empire. She might use her knowledge from the Clone Wars era to help the Rebels in unexpected ways, like teaching them some old Jedi combat techniques that were lost over time.
One idea could be a crossover with the original Star Wars trilogy characters. Maybe the Rebels crew teams up with Luke Skywalker and Han Solo to take on a new, powerful Sith threat. This would bring together the scrappy underdog feel of the Rebels with the classic heroism of the original trilogy.
In this fanfiction, Ezra could be on a mission and stumbles upon an ancient Mandalorian artifact. This artifact has some sort of connection to the Force, which draws Ezra in. As he delves deeper into the Mandalorian culture to understand the artifact, he uncovers secrets that not only change his perspective on the Mandalorians but also give him new powers or knowledge that he can use against the Empire. The story could explore how Ezra balances his newfound Mandalorian - influenced identity with his role as a rebel and a Force - user.
One idea could be that Ezra is kidnapped by the Empire. They might want to use him as bait to lure the other rebels. The rebels then have to come up with a risky plan to rescue him. Maybe they get some unexpected help from an old acquaintance of Ezra's.
One idea could be to have Naruto characters in the Star Wars Rebels universe. For example, Naruto could be a Jedi - like figure with his chakra being similar to the Force. He could use his shadow clone jutsu in battles against the Empire, creating distractions and overwhelming opponents. Sasuke could be a Sith - like character who is initially on the wrong side but later sees the light.
Perhaps Ezra is injured in a trap set by an Inquisitor. His injury not only affects his physical abilities but also his confidence. His friends, like Kanan, would have to help him regain his trust in himself and the Force. They might go on a journey to find a special healer or an ancient Jedi relic that could aid in his recovery, all while being pursued by the Empire.