A more complex plot could be that there's a mystery in the Valkyrie Drive world that only the OC and Lady J seem to be aware of. They have to work in secrecy to uncover the truth. Along the way, they discover secrets about each other's pasts that either bring them closer or create some initial tension between them.
One idea could be that the OC and Lady J are on a mission together in the Valkyrie Drive world. They face a powerful enemy and have to learn to combine their unique abilities to defeat it. Maybe the OC has a special power that Lady J initially doubts but then comes to rely on.
They could be forced into situations where they have to rely on each other. Say they get trapped in a dangerous area. The OC might be good at finding a way out, but Lady J is better at fighting off the threats in that area. Through this cooperation, their relationship can grow. Also, showing their flaws and how they accept each other's flaws is important for a realistic relationship development.
One common theme could be the clash of different worlds. Naruto's ninja world and Valkyrie Drive's world are very different, so exploring how the characters adapt to each other's worlds is often seen.
Well, you can try looking on some popular fanfiction websites like FanFiction.net or Archive of Our Own. Just search for 'naruto x lady j valkyrie drive' there and you might find some interesting stories.
A more complex plot could involve time - travel. Maybe an enemy from the past is brought to the present and is causing chaos. Peter and Valkyrie are brought together by Doctor Strange or some other powerful character to fix the timeline. They have to travel to different time periods, including Asgard in its prime and Peter's past in Queens. Along the way, they discover secrets about each other and the MCU universe as a whole.
Another plot could involve Nora somehow getting access to Naruto's chakra system. This could lead to her developing new powers similar to Naruto's. They might train together, with Nora teaching Naruto about the different Dust types in her world while Naruto shows her more advanced chakra control techniques. Their combined skills could then be used to face a powerful common enemy.
One idea could be that the OC is a healer who stumbles upon Frankenstein's monster in the woods. The OC decides to help the monster, despite the danger, and they form an unlikely bond. This could lead to a story of redemption for the monster and a journey of self - discovery for the OC.
Maybe the OC is a scientist who has developed a device that can temporarily steal The Flash's speed. At first, the OC uses it for personal gain, but then realizes the chaos it's causing in the city. They then team up with The Flash to take down other villains who are after the device. Or, the OC could be a meta - human with the ability to see the future in flashes. The Flash initially doesn't trust the OC, but as they start to have the same visions, they have to work together to prevent a major disaster from happening.
The OC could be a psychic who is unknowingly drawn to Derry because of Pennywise's presence. Their psychic powers allow them to sense Pennywise's energy but not fully understand what it is at first. As Pennywise tries to manipulate the OC, the OC starts to fight back using their psychic abilities, creating a battle of wills and powers that could span across different dimensions within Derry, from the sewers to the abandoned houses and the mindscapes of both characters.
The OC could be a researcher studying digimon behavior. Renamon becomes the subject of the study. At first, Renamon is very guarded around the OC. However, as the OC shows genuine respect for Renamon and her kind, Renamon begins to open up. They then embark on a journey to discover more about the history of digimon, with their relationship growing stronger along the way.
Well, an interesting plot could involve an OC that is a transfer student, just like the protagonist. But this OC has a hidden past related to the Metaverse. Maybe they were experimented on by a shadowy organization in their home country, and this gives them a different perspective on the Metaverse compared to the Phantom Thieves. Their goal could be to find out who was behind those experiments and get revenge. Along the way, they form a bond with the group and learn new ways of using their powers.