Their love story could be developed through a shared goal. Suppose there is a powerful and evil force that threatens both the ninja world and the supernatural world that Rias is from. Naruto and Rias have to work together to stop it. During this process, they rely on each other, share their fears and hopes. Naruto's loyalty to his friends is something Rias admires, and Rias' elegance and charm start to attract Naruto. Slowly, their feelings turn into love.
In the fanfiction, their love story could be set in a new world where both Naruto's and Rias' universes collide. Maybe Naruto is on a mission in Rias' world and they meet by chance. Naruto's unique powers like the Rasengan would be a novelty in Rias' world, and she would be intrigued. As they get to know each other, they start to care for one another, and love blossoms. It could also involve some cultural exchanges between the two different settings.
In a fanfiction, it could be that Haku is sent on a mission to Konoha undercover. Naruto, being the friendly and curious ninja he is, befriends her without knowing her true intentions. As they spend more time together, Haku starts to question her mission because she's falling for Naruto. Their love story could develop as Haku struggles with her loyalty to her original side and her new - found feelings for Naruto. Naruto, on the other hand, is just happy to have a new friend who he's slowly falling in love with.
One way the story could be developed is by showing Naruto's reasons for becoming a pickpocketer. Maybe he's desperate to help his village in some way and sees pickpocketing as a quick solution. For example, he could be stealing from the rich to give to the poor in Konoha. This would add a Robin - Hood - like aspect to the story.
In a fanfiction, it could be developed through mutual understanding. Naruto has always been an outcast, and Sakura could be the one to truly understand his loneliness. On the other hand, Sakura has her own insecurities, and Naruto could be the one to make her feel confident. As they open up to each other about their deepest feelings, love could gradually blossom.
The fanfiction might begin with a magical event that somehow links Naruto's world and Rias' world. This event could bring them together, and as they get to know each other better, they develop feelings for one another. Then, once they find out about the baby, they have to figure out how to deal with this new situation in the context of their two very different worlds.
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.
In this kind of fanfiction, it could be developed through shared traumas. Naruto, who has his own painful past, might find a connection with Itachi's complex and tragic backstory. They could start to understand each other on a deeper level during some missions or encounters where they have to rely on one another. Naruto's optimistic nature might start to break through Itachi's cold exterior, gradually leading to feelings of love.
One possible fanfiction idea could be that Rias' sick brother is a key factor in a power struggle within their supernatural world. Naruto, being an outsider with his own set of skills and values, could get involved. Maybe he forms an alliance with Rias to protect her brother from those who would use his illness to their advantage.
One way the story could be developed is that Naruto's death could trigger a chain of events within the Hidden Leaf Village. His friends, like Sasuke, might be filled with guilt and anger. Sasuke could vow to avenge Naruto and start a dark path of seeking extreme power. Meanwhile, the village would be in mourning, and the younger generation would see Naruto as a martyr, inspiring them to train harder to protect the village in his memory.
One way could be through some sort of magical or cross - dimensional event. Maybe a powerful magic user or a godly artifact messes up the fabric of different mythologies and universes, bringing Naruto and Aphrodite together. Naruto, with his strong sense of loyalty and justice, might initially be very confused by Aphrodite's beauty and the concept of Greek gods.
In a fanfiction where Naruto is the villain, perhaps he becomes corrupted by the Nine - Tails' power. The constant struggle to control the fox within him finally takes a toll, and instead of fighting it, he gives in. He then uses the Nine - Tails' brute strength to wreak havoc. He might see the shinobi world as a place full of hypocrisy and decides to 'cleanse' it by force, attacking villages one by one, starting with Konoha, which he now views as a place of false promises.