One great Ayra Stark x OC fanfic is 'The Journey with Ayra'. It has a well - developed OC character who embarks on an adventure with Ayra. The story is full of action and their relationship development is quite interesting.
There's also 'Ayra and the Mysterious Stranger'. In this fanfic, the OC is a bit of an enigma at first. As the story progresses, the connection between Ayra and the OC deepens in a very engaging way. It's got great descriptions of the world they are in, which really adds to the overall atmosphere.
Well, 'Ayra Stark's Unlikely Ally' is a fanfic worth checking out. The OC in this one has a unique backstory that ties in well with Ayra's own story arc. Their interactions are filled with both tension and camaraderie, and the plot keeps you hooked from start to finish.