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.
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.
One idea could be that the OC is a new Keyblade wielder who meets Ventus during his training. They start as rivals, constantly competing in battles and challenges. But as they face a powerful enemy together, they realize their combined strength and start to develop feelings for each other.
Maybe the OC is a time - traveler who accidentally lands in Obito's time. She knows about his future actions but instead of trying to stop him right away, she tries to understand his pain. This leads to a complex relationship where Obito is both intrigued and afraid of her knowledge.
One idea could be that the OC is a vampire hunter who initially sets out to destroy Dracula but ends up falling in love with him. Their relationship could be a struggle between her duty and her new - found feelings.
One idea could be that the OC is a new player in the game who gets accidentally transported to the world where Momonga is. Momonga, being curious about this strange new entity, decides to keep the OC close. They then embark on adventures together, with the OC showing Momonga different perspectives from a normal player's view.