It's possible that the OC is an artist or a musician themselves. They might be in the same industry as BTS and have interacted with them before. They respect BTS's talent and artistry, and when they see the threat of the shooting, they use their own resources and skills to save them. The OC could be someone who has connections to powerful people in the music industry and uses those connections to get help for BTS as well.
Maybe the OC is a new character who has a mysterious background. They could be from a different world or have some sort of special training that makes them capable of saving BTS. For instance, they could be a trained bodyguard from a secret organization.
Well, it could be that the OC has some sort of special power or ability. Maybe they can sense danger and so they step in just in time to stop the shooters from harming BTS. For example, the OC could be able to create a force field around BTS that deflects the bullets.
It could be a new character created by the author, like a young kunoichi from a small, far - away village. She might have special powers related to nature, like the ability to communicate with animals. This would make for an interesting dynamic when babysitting Naruto, as he's always been curious about different ninja abilities.
The OC could be a mysterious ninja from a far - off land. Sasuke might think this ninja has some secret knowledge about the Uchiha clan that he wants, so he kidnaps them.
The OC could be an outcast in the ninja world. They don't belong to any major clan and are constantly on the move. Hidan might see this OC as an easy target. The OC might have some unique skills, like being able to communicate with animals, but these skills are not enough to protect them from Hidan when he decides to sacrifice them for his own dark purposes.
Superman could also be a main character. He might be the one to first discover the oc after their rebirth. Superman's moral compass would lead him to either protect the oc or keep an eye on them depending on how the oc behaves. And his super strength would be a factor in any interactions with the oc.
It could be an exiled shinobi from a far - off land. Maybe they were wrongly accused in their own village and had to flee. They then come across Naruto and see in him the potential for change in the ninja world, so they decide to raise him with their own set of values.
Happy could be an interesting character. He could be like a sidekick and a source of comic relief during their relationship journey. For example, he might accidentally interrupt their romantic moments or give Natsu really bad advice on how to court the OC at the beginning. Erza could also be important. She could be the one who gives the OC advice on how to handle Natsu's wild nature, as she has known him for a long time.
Well, King Cold himself would surely be an important character. He could be portrayed as a strict and overbearing father figure, constantly pressuring the OC to be more like him. Frieza could also be a main character, perhaps as a jealous brother who sees the OC as a threat to his own position in the family hierarchy.
Love is a very common theme. Usually, it involves the OC falling in love with one of the BTS members. For example, in many fanfictions, the OC might be a regular girl who meets a BTS member and they gradually develop feelings for each other.
The OC master could be a hermit who has been living in isolation for years, developing a unique understanding of the Force. He or she might have witnessed the downfall of the Jedi Order in the past and wants to prevent Anakin from making the same mistakes.