You could also make an OC that is related to one of the existing characters in Majikoi. For example, a long - lost cousin of one of the main guys. This OC could bring a new dynamic to the relationships already in place, and perhaps even uncover some family secrets within the story of Majikoi.
One idea could be to create an OC who is a new transfer student at the school in Majikoi. This OC could have a unique skill, like being a martial arts expert from a far - off land. They would then get involved in the various clubs and rivalries at the school.
You could create an alternate universe where the characters have different abilities or roles. Maybe in this universe, the characters are part of a magical world instead of a normal school setting. This would change the dynamics between them and lead to new and exciting plotlines.
One idea could be exploring the backstory of one of the less - known characters in more detail. For example, you could focus on a side character's family history and how it impacts their actions in the present within the Majikoi Oh! Samurai Girl universe.
You could also create an OC who is a spy sent to infiltrate the Darkling's inner circle. The OC has to balance their mission with their growing feelings for the Darkling, which makes for a complex and engaging story.
Well, you could have an OC that is a skilled hacker who gets involved with the Phantom Thieves by accident. They might have a Persona that represents a famous code - breaker from history. Also, an OC who is a foreign exchange student from a country with a very different cultural background could bring in new elements to the fanfiction. Their Persona could be influenced by their home country's folklore. Maybe an OC who is a prodigy artist and uses their art skills to create powerful items in the Metaverse, with a Persona related to a great artist from the past.
One idea could be a Garou OC who is a lone wolf, not part of any pack, and has to survive in a world full of both human and supernatural threats. They could have unique powers like the ability to blend into shadows, which helps them in their solitary existence.
One idea could be to explore Imhotep's life before he became the mummy. Maybe he was a brilliant architect with a secret love interest that influenced his actions later. Another could be a story where an OC helps Imhotep break free from his curse in a different way than in the movies. For example, the OC has a special magical ability that can nullify the dark magic binding him.
Well, you could write a fanfiction about a Marvel OC who is from an alternate dimension where the roles of heroes and villains are reversed. This OC comes to the main Marvel universe to try and right the wrongs in their own dimension. Or perhaps an OC who is a young Asgardian with a gift for magic that Odin tries to keep hidden for some reason, and the OC has to navigate the politics of Asgard while also dealing with their emerging powers.
One idea could be an OC who is a spy sent to infiltrate Doflamingo's organization. This OC could have a hidden past that slowly gets revealed as they gain Doflamingo's trust. Another idea is an OC with a special power that Doflamingo wants to control or use for his own evil plans. For example, the OC might be able to manipulate time in a small area, which could be a great asset in battles or heists.
Another interesting concept is to create an arrancar OC who is an outcast among their kind. Maybe they have a unique power or appearance that makes the other arrancars shun them, and they have to find their place in the world.
You could write a fanfiction where your OC is a mutant with a unique power that Logan is initially skeptical of. As they interact more, Logan realizes the potential of this new power and they work together to fight a common enemy. For example, if your OC can manipulate time on a small scale, it could add an interesting dynamic to their adventures.