Levi Ackerman from Shingeki no Kyojin is also a very popular character to feature. His exceptional combat skills could be pitted against Naruto's ninja techniques. Maybe he could teach the Naruto characters some of his own unique combat strategies.
Eren is often a popular character in these fanfictions. Since he's a central character in the original series, in gamer fanfictions, he could be the one that the gamer teams up with or tries to influence. His strong will and determination make him an interesting character to include in these alternate stories.
One popular 'Shingeki no Kyojin' fanfiction is 'The Wings of Freedom'. It explores an alternate universe where Eren has different powers and the story takes a new turn. Another is 'Beyond the Walls' which focuses on the characters' lives outside the main events of the original series.
One popular story could be about an OC who has a unique ability that helps in the fight against the Titans. For example, an OC with the power to control the elements and uses it to protect the Survey Corps during their expeditions.
One idea could be a crossover where Naruto characters gain the ability to transform into Titans. For example, Naruto could use his chakra to control the Titan form in a unique way.
The exploration of the Titans' origin in a more detailed way is another common theme. Fanfic authors often come up with their own theories and stories about how the Titans were created and what their true purpose might be, adding new layers of mystery to the 'Shingeki no Kyojin' world.
In some fanfics, the themes of both series are blended. 'Shingeki no Kyojin' is about survival against overwhelming odds, and 'Naruto' is about achieving dreams and facing one's past. A fanfic could explore how the characters from both series deal with each other's problems. For instance, how would the ninjas of Naruto react to the despair and hopelessness that often fills the 'Shingeki no Kyojin' world? And how would the 'Shingeki no Kyojin' characters be inspired by Naruto's never - give - up attitude?
One interesting concept could be the combination of the unique power systems from both 'Shingeki no Kyojin' and 'Naruto'. For example, how the Titans' abilities might interact with ninja jutsus. Maybe the Survey Corps could use some Naruto - style stealth techniques to approach Titans more effectively. Another concept could be the character crossovers, like Eren Jaeger learning from Naruto about the power of friendship and how it can influence one's will to fight.
Most likely Eren would be one of the main characters as he is central to the original 'Shingeki no Kyojin' story. If the fanfic is about reading the future, his actions are often crucial in determining the fate of humanity, so he would be a prime candidate to have this ability or be affected by someone who does.
Some of the well - known characters from the 'Attack on Titan' series are likely to be main characters in this novel too. For example, Mikasa Ackerman might be one of them as she is a central female character in the overall story.
One possible plot could be that the ninjas from Naruto are transported to the world of Shingeki no Kyojin. Naruto and his friends could use their ninja skills to help the Scouts fight the Titans. For example, Naruto's Shadow Clone Jutsu could be used to create distractions while the Scouts attack. Sasuke could use his Sharingan to predict the Titans' movements. And Sakura could use her superhuman strength to take on the Titans directly.