You could also focus on the technology aspect. Templars are used to a certain level of technology in their world. How do they react to Xcom's advanced weaponry and high - tech facilities? Do they see it as a means to enhance their own abilities, or are they skeptical? This exploration of the relationship between different technological levels can add depth to the fanfiction.
One idea could be a crossover with the Mass Effect universe. The Xcom soldiers could encounter some of the alien races from Mass Effect and have to work together or face off against them. Maybe the Xcom team has to deal with the Reapers in some way.
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?
First, do some research on both the Xcom universe and the templar lore. Know their strengths, weaknesses, cultures, etc. Then, come up with a basic plot idea. For example, a group of templars could be accidentally transported to the Xcom world. After that, create your main characters from both sides and start thinking about how they'll interact.
One idea could be having the XCOM soldiers use their combat skills in the Mass Effect universe. Maybe they are sent to help fight against the Reapers. They could introduce their unique tactics and weaponry to the Mass Effect races.
Well, in 'xcom mass effect crossover fanfic', perhaps a cool concept is the interaction of the characters. Imagine Commander Shepard teaming up with XCOM operatives. They could share their combat strategies and knowledge. Also, the idea of using Mass Effect's biotics in XCOM missions or having XCOM's psi - ops in the Mass Effect universe could add a whole new layer of excitement to the story.
A plot could revolve around a rookie XCOM soldier who has a special ability that catches the attention of all the Chosen. They each try to sway the soldier to their side, and the soldier has to navigate through their offers while remaining loyal to XCOM. Or perhaps a fanfiction set in a parallel universe where the roles of XCOM and the Chosen are reversed, and we see how the Chosen fight against an oppressive XCOM - like force.
One popular xcom crossover fanfiction is the one where XCOM agents cross over with the Mass Effect universe. It's really interesting to see how the XCOM combat strategies are applied in the fight against the Reapers. Another great one is the crossover with the Warhammer 40K universe. The grimdark setting of 40K and the high - tech nature of XCOM create a really unique blend.
A plot could involve a conflict within the Templar Order regarding how to deal with the existence of the supernatural beings in Highschool DxD. Some might want to ally with them, while others see them as a threat to be eradicated. This could lead to an internal power struggle within the Order.
I really like 'XCOM in the Star Wars Galaxy'. It's a fun crossover where the XCOM troops are dropped into the Star Wars universe. They use their high - tech weaponry and tactics against the Sith and the Empire. It has some great battle scenes where XCOM's stealth technology clashes with the Force - using Sith Lords. Also, 'XCOM and Halo: The United Front' is quite good. The XCOM soldiers and the Spartans join forces to combat an alien invasion that is more powerful than either has faced before.
One interesting Xcom fanfiction could be about the soldiers' personal lives off - the - battlefield. For example, how they deal with post - combat stress and form relationships within the base. Another might be a story that reimagines the Xcom project from the perspective of an alien who has been captured and is trying to understand the humans' motives. There could also be a fanfiction where a new recruit has some sort of special power or ability that changes the dynamics of the Xcom team's missions.