One common theme is adventure. The Asura character often has a lot of power and abilities, and in the fanfiction, the reader might join Asura on some exciting adventures, exploring different worlds or fighting against powerful enemies.
Love and friendship are also quite prevalent. The relationship between the asura and the reader can develop into a deep friendship or a romantic bond. Sometimes, it shows how two very different beings can connect on an emotional level.
One of the themes is power dynamics. Asura is usually a very powerful character, and the OC may have different levels of power. How they balance this, whether the OC is weak and Asura protects them or the OC has a special power that complements Asura's, is often explored. Also, there is the theme of cultural exchange if the OC is from a different background than Asura's world.
I would recommend 'Asura's Embrace'. This fanfiction is notable for its detailed character descriptions. It really makes you feel like you are in the story, experiencing the emotions right alongside the characters. The writer does a wonderful job of building the relationship between Asura and the reader.
A sense of belonging is another big theme. The reader, who may feel like an outsider in the real world, finds a place where they belong among the mutants. There are also themes related to fighting for justice, just like the X - Men do in the original stories.
One common theme is adventure. Since Chekov is part of the Star Trek universe, many fanfictions involve the reader going on adventures with him through space, exploring new planets and facing various challenges.
Love and sacrifice are also very common. The reader might fall in love with Vergil and be willing to sacrifice for him, or vice versa. In some fanfictions, there is also the theme of discovery. The reader discovers new sides of Vergil that no one else has seen, which deepens their relationship.
One common theme is adventure. Since boboiboy is often involved in battles and saving the world, the reader character gets to be part of those exciting adventures in the fanfiction.
One common theme is growth. Both Armin and the reader often grow as individuals while their relationship also evolves. For example, they might learn to be braver in the face of danger.
One common theme is friendship. Since Fluttershy is a character known for her gentle and friendly nature, many fanfictions focus on building a strong friendship between her and the reader. Another theme is personal growth. The reader often helps Fluttershy overcome her shyness, and in the process, both characters grow.
A common theme is the exploration of Nico's character. Fanfiction writers often dig deep into Nico's personality, his insecurities, his strengths. And the reader character is usually the catalyst for this exploration. Another theme is the power of connection. Whether it's a romantic or platonic connection, it's shown to be very powerful. For instance, in some fanfictions, the connection between Nico and the reader is what saves them from a dangerous situation.