Maybe the story begins with a prophecy in the Naruto world about a powerful, otherworldly female coming. Meanwhile, in the Diablo universe, the female Diablo character is on the run from some powerful force. In her escape, she accidentally stumbles into the Naruto universe. Naruto's friends mistake her for a threat at first, but Naruto has a feeling she's not all bad, and he tries to protect her from his over - eager comrades, starting their journey together.
It could start with a strange rift opening up between the two universes. The female Diablo character is drawn through it and lands in the middle of Konoha. Naruto, being the first to encounter her, is both curious and cautious. He tries to communicate with her, but she's disoriented from the journey. This initial encounter sets the stage for their relationship, whether it will be one of friendship or enmity.
It could start with Naruto getting lost in an unknown forest. There, he stumbles upon the female orc's tribe. The orcs are initially hostile, but the female orc is curious about this strange human. She stops the others from attacking Naruto right away. This encounter would be the start of their story as they start to communicate, with Naruto using his charm and the female orc trying to figure out if he's a threat or not.
It could start with a strange rift in the space - time continuum that pulls Darth Sidious into the Naruto universe. Sidious would immediately start sizing up the situation, seeing the potential in the chakra - powered ninjas for his own power - hungry schemes.
The story could start with a strange portal opening in Gotham City. Out comes Naruto, all confused about this new and dark place. Harley Quinn, who was just about to cause some trouble, sees Naruto and is intrigued. She approaches him, not knowing what to make of this strange - looking boy with orange clothes and a headband.
One idea could be that a female Diablo character somehow gets transported to the Naruto universe. She might initially be seen as a threat, but then she teams up with Naruto and his friends to fight a common enemy. For example, a powerful demon that is causing chaos in both their worlds. Her unique powers from the Diablo universe could add an interesting dynamic to the battles in the Naruto world.
Mephisto could also be a great main antagonist. His ability to corrupt and manipulate could pose a real threat to Naruto. Mephisto might try to turn Naruto's friends against him or corrupt Naruto himself. Since Naruto values his comrades highly, this would be a difficult situation for him to deal with. And if Mephisto manages to get into Naruto's head, it could lead to some really intense and dark moments in the fanfiction.
One interesting plot could be Naruto being transported to the world of Diablo 3. He might initially be confused by the dark and demonic environment but quickly adapt his ninja skills. For example, his shadow clone jutsu could be used in unique ways, like sending clones to explore different areas filled with demons while he focuses on a main objective. His chakra could also be seen as a form of magic in the Diablo 3 world, and he could learn to combine it with Diablo - style spells or abilities.
It could start with Naruto being found in the Fairy Tail world as a baby, with Erza taking him in as her own. She might notice something special about him right away, like his strong will that reminds her of herself. Then as he grows up, he starts to show signs of both ninja and magic abilities, which puzzles everyone in the guild but also makes them excited to see what he'll become.
Maybe it begins with Padme having a prophetic dream about a strange warrior from another world, which is Naruto. Then she starts to search for this figure and eventually they meet in a rather unexpected place in the Naruto world.
It could start with Naruto being left out of a major village event. He feels really down and decides to go for a walk in the forest. Meanwhile, Yugito is passing through the area on her way to Konoha for some meetings. She spots Naruto looking sad and decides to say hello. That's the initial encounter that could kick off their story together.
One way it could start is that Rias is on a mission to explore different worlds for some reason related to the devil world. She accidentally ends up in Naruto's world. Naruto, being the curious and friendly person he is, offers to help her. As they journey together, they learn about each other's cultures and powers, and the attraction between them begins to grow, leading to a relationship and eventually marriage.