One idea could be to insert yourself as a new crew member on the Normandy. You could bring unique skills from your own world, like a special form of martial arts or advanced knowledge of technology that's different from the Mass Effect universe. Maybe you're an expert in ancient Earth cultures and can use that knowledge to help decipher Prothean artifacts in a new way.
You could also create a self - insert where you are a biotic with an entirely new form of biotic power. This power could be based on something from your real - life experiences or interests, like the ability to manipulate energy in a way that's related to music. Your character could then use this unique biotic ability to change the course of battles or diplomatic situations in the Mass Effect universe.
One interesting concept could be the exploration of how a self - inserted character interacts with the existing AI in the Mass Effect universe. For example, they might try to understand and even modify the AI's programming, leading to unexpected consequences.
Another great 'Mass Effect' SI fanfiction idea is when the self - inserted character is a former military officer from Earth. They use their combat experience and strategic thinking to make a name for themselves in the galactic military scene. This can lead to some really cool crossovers with the existing Mass Effect military organizations like the Alliance Navy.
A great Mass Effect crossover fanfiction idea could be a crossover with the Stargate universe. The Mass Effect races could discover the Stargate network and start exploring other galaxies through it. There could be conflicts and alliances with the various races in the Stargate universe. Also, a crossover with the Dragon Age series might be interesting. The mages and warriors of Dragon Age could interact with the biotics and soldiers of Mass Effect. They could learn from each other's magic and technology, and perhaps even fight together against a dark force that threatens both universes.
Relationships are also a big theme. The self - inserted character often forms relationships with the canon characters from the Mass Effect series. These relationships can range from friendships to romances. They add an emotional depth to the story and can also drive the plot forward as the character's decisions are influenced by their relationships with others.
First, decide on the character you'll be inserting. Think about their personality, skills, and backstory. Then, figure out how they'll fit into the Mass Effect universe. Are they going to be on the side of the Alliance, or maybe they'll be an independent agent? After that, come up with a starting point for your story, like arriving on a new planet in the Mass Effect galaxy.
One idea could be to have the Guardians from Destiny encounter the Normandy crew in Mass Effect. They could team up to fight a common enemy like a new, powerful alien race that has the technology to disrupt both the Traveler's Light in Destiny and the Mass Relay network in Mass Effect.
In a Prototype - Mass Effect crossover fanfiction, a possible scenario is that the Reapers from Mass Effect encounter Mercer. Since Mercer can consume and assimilate other beings, it would be interesting to see how he'd fare against the Reapers. He might be able to absorb some of their technology or even gain new powers from them. And the way the different races in Mass Effect, like the Turians or Asari, would react to his presence would also be a great plot point.
Another aspect could be the exploration of the political and cultural differences between the two universes. XCOM is mainly focused on Earth defense, while Mass Effect has a complex galactic political system. A fanfiction could explore how the two groups interact when it comes to things like trade, alliances, and dealing with common threats. For instance, how would the XCOM Council (if there was one in the crossover) deal with the Citadel Council's decisions and vice versa?
A great concept could be a story where the Prototype technology is somehow introduced into the Mass Effect universe. For example, some Cerberus scientists could get their hands on Prototype samples and start experimenting. This could lead to the creation of new, dangerous hybrids that the main characters have to deal with. Or perhaps Shepard has to team up with a character similar to Mercer to fight a common enemy that is exploiting both Prototype and Mass Effect technologies.
One idea could be the Pilots from Titanfall teaming up with the Normandy crew in Mass Effect. They could share their combat skills and technology. For example, the Pilots' parkour abilities might amaze the Mass Effect characters, and in return, the advanced biotics and tech of the Mass Effect universe could be useful for the Titanfall side.