One common theme is redemption. Often, the OC is used to give Bertholdt a chance at redemption for his actions in the original series. Another theme is friendship. The OC forms a strong bond with Bertholdt, showing a different side of his personality.
Love can also be a theme in some Bertholdt OC AOT fanfiction. It could be a romantic love between the OC and Bertholdt or a platonic love that still has a strong impact on their characters. This love can be a driving force for change in Bertholdt's character, as he learns to care for someone other than his original comrades in a different way.
Some fanfics also focus on the psychological aspect of their relationship. Reiner and Bertholdt both have complex personalities and backstories. Fanfics might explore how they understand and support each other on a psychological level, perhaps dealing with their inner demons together.
One great Bertholdt OC AOT fanfiction is 'The Hidden Potential'. It delves into a new character's journey alongside Bertholdt in the world of Attack on Titan. The story has really interesting character interactions and a unique take on the AOT universe.
One characteristic is the exploration of his relationships. In fanfics, we can see his relationships with other characters like Eren or Reiner developed in different ways. Some fanfics might make him more of a hero figure, while others might show his darker side more prominently. His transformation abilities are also often a key element in fanfics, with stories exploring how he controls or is affected by his titan form.
Another theme could be redemption. If Bertholdt has done some controversial things in the original story, fanfiction might explore his journey towards redemption with Jean being a part of that process, perhaps helping him or being a witness to his change. This often involves a lot of emotional exploration and character growth for both of them.
One common theme is loyalty. Given their situation in the military and the secrets they hold, their loyalty to each other is often explored. Another is the theme of unspoken feelings. They both seem to have deep emotions that they don't easily express, and fanfics often play around with that.
One popular 'AOT Bertholdt' fanfic is 'The Unseen Side of Bertholdt'. It delves into his inner thoughts and struggles during his time in the story. Another great one could be 'Bertholdt's Redemption Arc', which imagines a different path for him where he tries to make amends for his actions. There's also 'A Day in Bertholdt's Life' that gives a detailed account of an ordinary day from his perspective.
A very common theme in AOT time travel fanfiction is redemption. Characters who made mistakes in the original storyline get a chance to go back and make things right. Also, the exploration of alternate timelines is quite popular. Writers like to show how different choices made during time travel can lead to completely different outcomes for the AOT world. It adds an element of mystery and 'what - if' scenarios that readers find really engaging.
Survival and hope are also prevalent themes. Since the original Attack on Titan story is quite dark, in alternate endings, fans often write about how the characters find hope in the most desperate situations and strive for survival in different ways. For instance, they might find new methods to deal with the Titans or new ways to build a future for humanity that doesn't involve constant bloodshed.
One common theme is loyalty. Given their roles in the story, fanfictions often explore how loyal they are to each other, whether it's in the face of danger or moral conflict. For example, in many stories, they will stick together no matter what decisions they have to make.
The theme of trust is crucial in 'Attack on Titan Reiner x Bertholdt fanfiction'. They have to trust each other completely in order to survive in the harsh world of Titans. Additionally, the theme of redemption sometimes shows up. If they make mistakes or have actions that they regret, they try to redeem themselves in the eyes of each other and also within the context of their friendship.