A wizard or sorcerer from a different magical order than the one Doctor Strange belongs to. This OC could have their own set of spells and powers. They cross paths with Thor and decide to help him. Their magic could be used in creative ways, like creating illusions to deceive Thanos' minions or strengthening Thor's weapon with magical enchantments.
Maybe an alien from a planet that was previously unmentioned in the MCU. This alien OC has a special connection to the power of the Infinity Stones and teams up with Thor because they realize that Thor is a key figure in the battle against Thanos. Their knowledge of the Stones could be crucial in the fight.
One interesting concept could be how an original character (OC) interacts with Thor during the events of Infinity War. Maybe the OC has a unique power that helps Thor in his quest against Thanos, like being able to manipulate time briefly to give Thor an advantage in a battle.
Another theme is the OC's relationship with the established Avengers characters. Some fanfictions focus on the OC forming friendships, romances, or rivalries with the likes of Iron Man, Captain America, etc. It adds a new layer of drama to the Infinity War story. For example, an OC might start off as a fan of Tony Stark and then end up having to work with him during the war. The dynamic between them can be very interesting.
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.
One potential role could be a love interest. They might fall in love with one of the Avengers, like Black Widow or Hawkeye, adding a romantic sub - plot to the story. Another role could be as a mentor. If the OC is very experienced in a certain area, like ancient magic, they could teach Doctor Strange new things.
One great 'Avengers Infinity War OC fanfiction' is 'The New Hero in Infinity War'. It features an original character who has unique powers and gets involved in the events of the movie in an interesting way. The author does a great job of integrating the OC into the existing storylines.
Aang could be an ally. Despite the OC being Ozai's son, Aang, with his forgiving nature, might see the potential for good in the OC. He could help the OC to understand the importance of balance and peace.
Ruby could be a great ally. She's friendly and always open to new people. Her combat skills and leadership in Team RWBY could also benefit the OC. Plus, her positive attitude might inspire the OC in their Gamer - related adventures.
Start with a strong concept. It could be something like the OC being from another dimension and getting stuck in the Avengers' world. Then, build the story around that. Focus on the character development of both Thor and the OC. Let their relationship grow organically. Also, include some of the other Avengers to make it feel like a part of the whole universe. Write engaging dialogue and exciting action scenes to keep the readers hooked.
One great Thor x OC Avengers fanfiction is 'A New Ally'. It has an interesting plot where the OC has unique powers that catch Thor's attention. The story does a great job of integrating the OC into the Avengers' world.
One inspiration could be to focus on an original character's unique abilities. For example, if your OC has the power to manipulate time, they could be in a race against it during the events of Infinity War. They might try to stop Thanos before he gets all the Infinity Stones by using their time - altering powers in creative ways.