Well, a great plot for Gears of War Berserker fanfiction could involve a group of soldiers who discover a young Berserker that seems to have some level of intelligence. They try to train it or at least understand it. Another could be set in a post - apocalyptic world where the Berserkers have evolved further and the main character has to figure out their new abilities to survive. And, a third option is a story about a scientist who was involved in creating the Berserkers and now has to face the consequences when one gets loose in his lab.
In Gears of War Berserker fanfiction, you could write a story where a Berserker forms an unexpected bond with a small child. The child is not afraid of it and the Berserker, in turn, protects the child from other threats. Another idea is to have a fanfiction where the technology to control Berserkers is discovered and there is a power struggle over who gets to use it. Also, a story about a group of resistance fighters who use the Berserker's natural instincts against their creators would be quite interesting.
One idea could be exploring the origin of the Locust in more depth. Maybe there was a scientific experiment gone wrong that led to their creation. Another could be a story where a human and a Locust form an unlikely alliance to fight a common, greater threat within the Gears of War universe.
One interesting idea could be exploring the backstories of the minor characters. For example, the life of a regular Gear soldier before the war, how they were recruited, and their families. Another idea is to create an alternate universe where the Locust and humans form an alliance against a new common enemy. It could change the whole dynamic of the Gears of War world.
A plot idea could involve Kait forming an unlikely alliance. For example, she teams up with a former enemy who has some unique knowledge or ability. This alliance could lead to a series of adventures as they try to stop a new, powerful enemy. Also, a story about Kait's inner struggle with the dark secrets she's uncovered would be engaging. She could be torn between using the knowledge for good or being corrupted by it.
Perhaps they find a lost technology that could change the future of their world. Sam wants to use it for the good of all, but Anya is more cautious. This difference in opinion causes some friction between them at first. But as they face external threats who also want the technology, they learn to work together and reconcile their differences.
For Gears of War 4 crossover fanfiction, a crossover with the Star Wars universe would be really exciting. The Gears' tough and gritty combat style against the backdrop of the Star Wars galaxy. The Jedis and Siths could interact with the Gears in various ways. Maybe the Gears would get involved in a conflict between the Galactic Republic and the Separatists, using their own brand of weaponry and tactics.
One idea could be to explore the backstories of the minor characters in the Gears of War universe. For example, you could write about how a particular soldier got recruited into the COG. Another idea is to create an alternate timeline where the Locust invasion happened differently. Maybe the COG discovers a new weapon early on and changes the course of the war. You could also focus on the relationships between the characters outside of combat, like how they unwind and deal with the stress of the war.
One idea could be to have the Swarm characters interact with the Gears of War protagonists in a post - apocalyptic city. They could form an uneasy alliance to fight a new, even greater threat. For example, a powerful new enemy that is immune to the weapons they currently have.
One idea could be to have the Spartans from Halo team up with the COG soldiers from Gears of War to fight a common enemy like a new alien race that combines the threats of the Covenant and the Locust. They could exchange combat techniques and weaponry, leading to some epic battles.
One idea could be to have the characters from Gears face the same kind of epic battles as in God of War. For example, the COG soldiers could find themselves in a world full of Greek mythology elements. Maybe they have to fight alongside Kratos against some new, powerful monsters that are a mix of the grotesque creatures from Gears and the mythological beasts from God of War.
For Gears of War Berserker fanfiction, Cole Train could be a great addition as a main character. His charisma and combat skills would make for an exciting story. Dom Santiago is also a possibility. His loyalty and determination could be explored in the context of facing Berserkers. And of course, the Locust Queen. If the fanfiction delved into the origin of Berserkers, she could be a central figure.