A more emotional plot could be that Midnight has some knowledge about Naruto's parents that she hasn't shared yet. As they get to know each other better, she reveals bits and pieces about his parents' past, which helps Naruto understand his heritage on a deeper level. This could also lead to Naruto using some of the things he learns from Midnight to become an even stronger shinobi.
One idea could be a training arc where Naruto seeks out Midnight for some unique jutsu training. Since Midnight has her own special abilities, she could teach Naruto some new ways to use his chakra in unexpected situations. For example, she might show him how to use his shadow clones in a more stealthy way, similar to how she uses her own techniques to surprise opponents.
One idea could be that Midnight and Angel are on a mission together and they discover a hidden power that only works when they combine their magic. Another could be a story where they have to overcome their differences in magic types to save the Fairy Tail guild from a powerful enemy. Maybe they start off as rivals but gradually fall in love during their adventures.
One idea could be that Midnight uses his magic in a new and unexpected way to save Erza from a powerful enemy. This would show a different side of his character, perhaps a more heroic one. Another plot could involve them going on a quest together to find a rare magical item that has the power to change the fate of Fairy Tail. During the quest, they could face various challenges that test their relationship and individual strengths.
One plot idea could be that the reader is a new mage in the Fairy Tail guild and Midnight takes an immediate interest in their unique magic. He then offers to train the reader, and during the training sessions, they develop a deep bond and face various challenges together within the guild.
A third plot could be that the reader is sent on a mission to infiltrate Midnight's guild. However, as the reader gets closer to Midnight, they start to have second thoughts. Midnight, who is very perceptive, senses the reader's internal conflict. Instead of turning the reader in, he decides to help the reader complete their mission in a way that doesn't harm his guild. This act of kindness makes the reader see Midnight in a new light, and a relationship begins to form.
A plot could revolve around Sesshomaru being intrigued by Naruto's determination. Sesshomaru decides to train Naruto in some of his own combat techniques, which Naruto adapts to his own fighting style. In return, Naruto shows Sesshomaru the value of friendship and loyalty within a village. This could lead to Sesshomaru having a change of heart about his own solitary ways. Also, they could team up to face a common foe from Sesshomaru's world that has somehow entered the Naruto universe.
One idea could be that Naruto and Kashuina meet during a mission outside of Konoha. They start off as rivals, constantly trying to outdo each other in combat skills. But as they face various challenges together, they gradually develop a mutual respect and then deeper feelings. Another plot could be set in a post - war scenario where Naruto, now a hero, meets Kashuina who has a unique ability to heal the psychological scars of the war - torn ninjas. Their interaction then leads to a romantic relationship. And a third idea is that they are both students under a new sensei who pairs them up for special training. During this training, they discover things about each other that they never knew before and fall in love.
One idea could be Naruto being sent to the world of Death Note. He could use his ninja skills to try and outwit Light Yagami. Maybe he would initially be confused by the Death Note's power but then use his determination to stop Light from his killing spree. Another plot could involve Naruto meeting the Shinigami. He might learn about the balance between life and death in this new context and try to find a way to bring some of his ninja world's values to this strange new world.
Perhaps Naruto and Lala meet during a mission where Naruto is sent to a different dimension. Lala, being from an alien world, is intrigued by Naruto's determination and they form an alliance to face a common enemy in that dimension. Their different powers and abilities complement each other, and as they work together, they start to develop feelings for each other.
A more complex plot could be that there is a prophecy in both worlds about a union between someone from the Naruto universe and someone from Ruby's universe. Naruto and Ruby are the ones fated to fulfill this prophecy. They initially don't get along but as they face various challenges together, they start to understand each other and fall in love, while also saving both their worlds in the process.
In a naruto x avatar fanfiction, there could be a scenario where the Akatsuki from Naruto's world teams up with some of the villains from the Avatar world. This would force Naruto and the Avatar (whichever one it may be) to put aside their differences and form an alliance with other characters from both worlds to stop this powerful and evil coalition.