Another popular trope is'reverse engineering the Reapers'. In these fanfictions, the races in the Mass Effect universe try to understand and use Reaper technology against them. It often leads to some really cool technological advancements in the story and new ways to fight the Reapers that add an exciting element to the plot.
I really liked 'When Reapers Met the Ancients'. This fanfiction has a crossover between the Reapers and an ancient civilization in the Mass Effect world. It delves deep into the lore of both and how their meeting could change the course of the entire universe. It's a long read but definitely worth it for those who love exploring the deeper aspects of the Mass Effect universe.
One popular trope is the 'fish out of water' scenario. For example, a character from Mass Effect Andromeda suddenly finding themselves in the Halo universe or vice versa. They have to adapt to the new rules, technology, and culture. Another common trope is the 'power - up' trope. A character might gain new abilities by combining the technology or powers from both universes, like using biotics with Spartan armor enhancements. And of course, the 'enemies to allies' trope is popular too, where the normally opposing forces in each game, like the Krogan and the Covenant, have to work together against a greater evil.
One popular theme is rebuilding. After the destruction of the Reaper War, characters often focus on rebuilding their civilizations, whether it's the Citadel races or those on the fringes. Another theme is dealing with trauma. Many survivors have PTSD from the war, and fanfictions explore how they cope. Also, exploration of new technologies discovered during or after the war is common, as races try to use these to better their futures.
The 'Team - up Against a Greater Threat' trope is quite prevalent. For example, in Halo, different UNSC factions and even some Covenant remnants might join forces to face a new, more powerful alien threat. In Mass Effect, various species from different planets could unite against a new Reaper - like enemy. The 'Redemption Arc' is also seen often. A character who has made bad choices in the past, like a mercenary in Mass Effect, might try to make amends. In Halo, a disillusioned Covenant soldier could turn against his own kind and seek redemption.
One idea could be that Naruto is somehow transported to the Mass Effect universe and has to face the Reapers. His ninja skills might give him an edge in combat against the Reapers' minions. He could use his shadow clones to confuse the enemies and his rasengan as a powerful attack. For example, he might be able to take out a group of husks with a well - timed rasengan.
This fanfiction title 'naruto is a reaper mass effect fanfiction' seems really interesting. It could mean that Naruto has been reimagined as a reaper in the Mass Effect universe. Maybe his ninja skills are translated into some kind of combat or stealth abilities that are useful for a reaper - like character. It could also be about how Naruto's backstory and growth as a character in his original series would affect his actions and decisions if he were a reaper in Mass Effect. For example, his determination to protect his friends could be turned into a motivation to protect certain species or planets in the Mass Effect galaxy.
The unique blend of universes. When Mass Effect 3 is crossed with another fandom, like Star Wars for example, it creates really interesting scenarios. You can have Shepard and the crew interacting with Jedi or Sith, which is just super cool.
One popular 'Mass Effect Crossover Fanfiction' is the one where Shepard crosses over into the Star Wars universe. It's really interesting to see how Shepard's combat skills and leadership play out in a galaxy far, far away. Another is the crossover with the Halo universe, where the technology and species from both universes interact in unique ways.
The Reapers in Mass Effect are ancient, sentient machines. The original Reaper story involves their cyclical destruction of advanced civilizations. They were created by the Leviathans. Their purpose seems to be to cull the galaxy's civilizations at intervals to prevent chaos. They lie dormant for long periods and then emerge to carry out their grim task.
Liara T'Soni can also be a great character to feature. Her knowledge of the Protheans could be crucial in a fanfiction. Maybe she discovers a hidden Prothean weapon that could turn the tide of the war against the Reapers.