One interesting concept could be the crossover of characters. For example, imagining Shepard from Mass Effect in the Gears of War universe facing off against the Locust horde. It would be fascinating to see how his biotic abilities would interact with the brute force combat of the Gears of War world.
One interesting concept could be the combination of the high - tech elements from Mass Effect with the historical setting of World War 2. For example, imagining Shepard - like characters using biotics in the battlefields of WW2. It might also involve the races from Mass Effect, like Turians or Asari, interacting with the human factions of WW2 in unique ways.
One interesting concept could be the combination of different species from the Mass Effect universe in unexpected ways. For example, seeing a Krogan and a Salarian working together in a situation that defies their usual cultural norms. Another concept might be the introduction of new technologies or powers that blend the characteristics of different Mass Effect races.
Survival is also a big theme. Characters from both universes are often thrown into situations where they have to fight for their lives against new and powerful enemies. They need to use their skills, whether it's the strategic thinking of Mass Effect characters or the brute force combat skills of Gears of War characters, to stay alive.
One interesting concept could be the unique ways the slip drive is utilized in the fanfic. Maybe it's used for faster-than - normal travel to unexplored regions in the Mass Effect universe.
A great plot twist might be that the Reapers from Mass Effect somehow end up in the Gears of War world. The Locust could initially see them as allies against the humans, but then the Reapers turn on them as well. It would create a chaotic situation where the Gears of War characters have to team up with some of the Mass Effect races they previously didn't trust to fight a common enemy that is far more powerful than anything they've faced before.
There's also 'The Hybrid War'. In this fanfiction, the technology from Mass Effect and the combat style of Gears of War blend in a fascinating way. The author does an excellent job of creating a new world where the two franchises co - exist. It has a lot of twists and turns that keep you hooked from start to finish.
The evolution of AI is also a common concept. Fanfiction writers may imagine how Mass Effect AIs could evolve over time, perhaps developing new forms of intelligence or abilities that are far beyond what was seen in the game. This could lead to all kinds of exciting storylines, such as AIs becoming the saviors or destroyers of the galaxy.
One interesting concept could be the exploration of different relationships between characters that were not fully developed in the game. For example, the friendship or rivalry between minor characters.
Some interesting concepts include character development. Imagine a Spartan from Halo teaming up with a Spectre from Mass Effect. How would their training and personalities clash or complement each other? Additionally, the idea of the Forerunners' technology being studied by Mass Effect's scientists is quite cool. It could potentially change the balance of power in the Mass Effect universe and open up new plotlines for fanfiction writers.
One interesting concept could be the combination of Mass Effect's advanced technology with Naruto's ninja abilities. For example, imagine a character using biotics (from Mass Effect) while also performing ninjutsu. It might create some really unique combat scenes.