One plot idea could be that the OC is a scientist in the Terraformar world and has to study the Roach. During the study, they develop an unexpected bond. Maybe the Roach shows signs of intelligence that the OC discovers, leading to a friendship that goes against all the norms of that world.
Perhaps the OC has a special ability that the Roach is attracted to. For example, the OC can emit a certain frequency that calms the Roach. This leads to the Roach following the OC around. The story could then revolve around how the OC uses this connection to try and bring about some change in the relationship between humans and Terraformars, with the Roach as a key factor in that change.
A plot could involve the OC being lost in the Terraformar territory. A Roach finds the OC and instead of attacking, it protects the OC from other threats. As time passes, they rely on each other for survival and form a unique relationship. The OC might then try to find a way to communicate with the Roach on a deeper level.
Think about the OC's goals. If their goal is to find a way to coexist with the Terraformars, especially the Roach, it gives them a clear motivation. They could be constantly learning about the Roach's behavior and trying different ways to communicate. Also, give them relationships with other characters in the fanfiction world. Maybe they have a mentor who warns them about getting too close to the Roach, but they don't listen because of their determination.
One idea could be that Naruto is on a mission in a strange land where the locals are obsessed with Papa Roach's music. He has to sing 'Burn' as part of a ritual to gain their trust and get the information he needs for his mission.
One idea could be that the OC, as the son of Hades, struggles with the stigma associated with his father's realm. He could be trying to prove that he's not all about death and darkness. For example, he might use his powers to help the living in secret, like saving people from disasters that are on the verge of happening.
Perhaps an OC is a young archaeology student who idolizes Nathan Drake. They manage to get involved in one of his expeditions through sheer determination. Along the way, they learn from Drake and also teach him new things about modern archaeological research methods. It could be a story of growth and adventure for both characters.
The soothsayer OC could be from a long - lost clan that was exiled from the village in the past. Their ability to see the future makes them a target for some who want to use their power for evil. In the fanfiction, they form an unlikely alliance with Naruto. He helps protect them from those who would harm them, and in return, the OC uses their foresight to help Naruto in battles and make important decisions for the village.
One idea could be an oc (original character) who has a special bond with the Ten - Tailed Beast. Maybe the oc is a descendant of an ancient clan that was once tasked with protecting the beast. The story could follow their journey as they try to keep the beast hidden from those who would misuse its power.
A plot could involve the mute OC being a new transfer student in the school. Their muteness makes them an object of curiosity and some characters might initially misjudge them.
One idea could be that the male OC is reborn into the Uzumaki clan during a time of great turmoil. He could use his knowledge from his past life to help the clan survive and thrive. Maybe he knows about upcoming threats and can prepare the Uzumaki for them.
One idea could be an OC who is a lightning - style user in Kumogakure and has to face a powerful enemy from another village. The OC could discover a new jutsu during the battle.
A story about an OC who is a healer in the Injustice 2 world could be really engaging. In a world full of battles and destruction, this OC could be trying to heal not only the physical wounds but also the emotional and psychological damage that the characters have endured. They might face challenges like being kidnapped by villains who want to use their healing powers for their own evil purposes.