Here's a more complex plot idea. An OP OC is actually a reincarnation of an ancient and powerful being. As they gradually regain their memories and powers, they face opposition from different factions in the Against The Gods world. Some fear their power, while others want to use them for their own gain. Meanwhile, the OC is trying to figure out their true identity and purpose, and they also form unexpected alliances along the way. This plot can explore themes of identity, power, and destiny in the context of the Against The Gods fanfiction.
One plot idea could be an OP OC who is from a different dimension and accidentally ends up in the Against The Gods universe. Their strange powers disrupt the existing balance, and they must either adapt or be hunted down. Another idea is an OC who is born with an OP ability but is shunned by society because of it. They then set out on a journey to prove their worth and change the perception of such powers in the Against The Gods world.
To create a compelling OP (Overpowered) or OC (Original Character) in Against The Gods fanfiction, first, understand the world's rules and power system. Then, give your character a unique backstory that ties into the existing lore. For example, if the world has a magic system based on elements, your character could have a tragic past related to a misuse of a certain element. This would not only make the character interesting but also give them motivation.
One plot idea could be an OC who is a reincarnated angel in the Highschool DxD world. The OC has to hide their true identity while trying to stop a secret group of devils from starting a war between the three factions. They could team up with Issei and his friends, but there would be constant suspicion from the devils around them.
One idea could be an OC with a unique sacred gear that has powers no one has seen before. For example, a sacred gear that can manipulate time on a small scale, allowing the OC to freeze time briefly during battles in Highschool Dxd's universe. This would add a whole new dynamic to the battles and interactions.
One idea could be an OC who discovers a unique Devil Fruit that gives the power to manipulate time in a very limited area. This could lead to all sorts of adventures as they try to keep it a secret from the wrong people in the One Piece world. Another could be an OC with a Devil Fruit power that allows them to communicate with ancient sea creatures, which could help in finding hidden treasures.
One idea could be that the male OC has a unique semblance related to time manipulation. He could use it to outwit the villains in RWBY's world. For example, he might freeze time briefly during a battle to analyze the enemy's moves and then counterattack effectively.
Well, a plot could involve an OC who is a gamer and a big fan of Dxd. They end up in a junkyard where they accidentally open a portal to the Dxd realm. Since they are a gamer, they quickly adapt to the new world and use their gaming skills to become OP. They could start by forming alliances with different factions in the Dxd world and use their junkyard - found items as unique weapons or tools.
Well, you could have an OP OC who is a master of ancient magic. He could use this magic to outwit the devils, angels, and fallen angels in the DxD universe. Maybe he has a secret past that ties him to an ancient prophecy, and as he discovers more about it, he has to face powerful enemies. You can also focus on his relationships, like having a romantic interest with a character from the original series that changes the power dynamics between different factions.
One idea could be creating an OC (Original Character) who is a descendant of one of the main characters in 'Seven Deadly Sins' and has a unique power related to one of the sins. For example, an OC who is a descendant of Meliodas and has a power that is a variation of his 'Full Counter' ability but is related to the sin of wrath. Another idea is to make an OC that is from a different kingdom entirely and has to deal with the chaos caused by the Seven Deadly Sins. They could start off as an antagonist but later realize the true nature of the sins and join them.
Well, you could make an OC that is a half - angel, half - devil. This would give the character a very complex backstory and internal conflict, especially in the world of Highschool DxD where the angels and devils have their own politics and power struggles. Also, for the OP part, this OC could have a special ability to combine angelic and demonic powers in a new and powerful way.
One idea could be an OC who is a gamer in the modern world suddenly gets transported into the Fate Stay Night universe during the events of the opening sequence. They could use their gaming knowledge, like strategic thinking and quick reflexes, to survive and make an impact on the Holy Grail War.