Friendship is also a theme that often shows up. The male reader might start as Mikasa's friend and then the relationship could develop into something more. Redemption is another one. Maybe the male reader has a past mistake and through his relationship with Mikasa, he finds a way to redeem himself. Also, the theme of survival in the harsh world of Attack on Titan is quite common in these fanfictions.
One common theme is adventure. Since the world of Attack on Titan is full of danger, many fanfictions will have the male reader and Mikasa going on dangerous missions together. Another theme is loyalty. Mikasa is very loyal in the original story, and this trait often carries over into the fanfictions, with her being loyal to the male reader as well.
A theme of family and loyalty often emerges as well. Since Mikasa has a strong sense of loyalty to her friends and comrades in the original series, this can be extended to her relationship with the male reader. They might become like family to each other, and the fanfiction could explore how that bond deepens over time and through various challenges.
One common theme is protection. Mikasa is a strong character, and in many fanfictions, she is shown protecting the reader from various threats. For example, in fictions set during battles or dangerous situations.
Another theme is isolation. As a vampire, she may be different from those around her, whether it's her friends or the human society she used to be a part of. This can lead to her feeling alone and having to find her place in the world.
Often, survival is a theme. Given the nature of the original story they are from, fanfictions might show how Jean and Mikasa rely on each other to survive in difficult situations. Also, loyalty is a big theme. Their loyalty to their comrades and to each other can be a central focus, with stories exploring how far they would go to protect one another.
One common theme is the exploration of their relationship in a world full of danger. Since they are both in a harsh environment, their bond can be a source of comfort and strength.
One common theme is trust. Given their respective personalities, they both have to learn to trust each other in many fanfictions. For example, in stories where they are on a dangerous mission together, they need to trust the other's combat skills and decision - making abilities.
A common theme is loyalty. Both Mikasa and Levi are known for their loyalty in the original story, and in fanfictions, this loyalty often extends to their relationship with each other, whether it's loyalty on the battlefield or in more personal situations.
One common theme is role reversal. Since Mikasa is often portrayed as a strong, protective figure in the original, making Mikasa male in these fanfictions often emphasizes that role even more towards female Eren. Another theme is the exploration of different gender dynamics. For example, how a male Mikasa might court or show affection to female Eren in ways different from the original dynamic.
Friendship is a common theme. Since they are comrades, many fanfictions explore how their friendship could develop into something more. For example, they might start to rely on each other in different ways than just as fellow soldiers.