One idea could be a story where Aatrox, the Darkin Blade, and Fiora, the Grand Duelist, are forced to team up. Maybe there's a greater threat to their world that only their combined skills can face. They start off distrusting each other, but as they face challenges together, they gradually come to respect one another's abilities.
Another plot could be a fanfic set in an alternate universe. Aatrox is not a menacing Darkin but a lost soul, and Fiora discovers him. She decides to help him find his true purpose. Along the way, they have duels not to harm each other but to test their limits and grow stronger together. This could lead to a deep emotional bond between them.
A third plot idea is that Fiora, in her pursuit of the perfect duel, hears rumors of Aatrox's incredible power. She seeks him out to challenge him. Aatrox, initially dismissive, is intrigued by Fiora's tenacity. As they duel, they realize they have more in common than they thought, and the fight becomes a dance of blades and mutual understanding, leading to an unexpected friendship or more.
The plot might involve Aatrox being intrigued by Fiora's unwavering courage. He could see in her a potential to be a great warrior on his side, not as a minion but as an equal. So he tries to persuade her to join his cause, which leads to a series of intense dialogues and battles between them, as Fiora is hesitant but also curious about Aatrox's power.
For Fiora, you can focus on her noble upbringing and her sense of honor. Show how these traits influence her actions when she meets Aatrox. For example, she might be disgusted by Aatrox's use of dark magic but also respect his power.
For Aatrox, you could focus on his past as a Darkin. His internal struggle between his dark nature and any glimmers of his former self could be explored. Show how Fiora's presence either exacerbates or soothes this conflict. For Fiora, her pride as a duelist is key. You can show how she reacts when faced with Aatrox's power that might be greater than what she's used to. Does she become more determined or is she momentarily daunted?
Perhaps a fanfic where Aatrox, in his more sentient moments, is intrigued by Irelia's unwavering will and spirit. He decides to test her, not as an enemy but as a way to understand the concept of hope that she represents, leading to a series of duels and philosophical exchanges between them.
A plot could involve a time - travel scenario. Lissandra, in her quest for power or knowledge, accidentally sends herself back in time to a period when Aatrox was at his peak of power. Aatrox initially sees her as a threat but then realizes she might be useful in his own plans. They form an uneasy alliance, and during their time together, there are moments of conflict, cooperation, and perhaps even a hint of something more than just a strategic partnership.
The theme of self - discovery is also quite common. Through their relationship, both Fiora and Riven may learn more about themselves. In some fanfics, Fiora discovers a new side of herself as she gets to know Riven better. And Riven may come to terms with her past and her identity through her bond with Fiora.
One idea could be a crossover where Naruto's world and the world of X - 23 from the X - Men collide. Maybe X - 23 is on a mission and accidentally ends up in the Hidden Leaf Village. She has to learn to adapt to this new place with its different culture and ninja ways. Naruto could be intrigued by her and her abilities, and they could team up to face a common enemy.
One idea could be a story where Spiderman has to team up with his greatest enemies to fight a new, more powerful threat from outer space. This would force him to put aside his differences and find common ground with the likes of Doctor Octopus and Green Goblin.
A theme that often appears is the power struggle. Given that they both seem to be strong characters in their own right, fanfics might explore how they deal with power dynamics between them. Maybe they compete at first and then realize they can be stronger together. It's also possible to see themes related to loyalty and betrayal. For instance, they might have to choose between their loyalty to their factions and their feelings for each other in some fanfics.
One popular Fiora x Riven fanfic is 'The Duelist's Bond'. It explores their relationship in a world filled with challenges. They start as rivals but gradually develop a mutual respect that could potentially turn into something more. The story is full of great fight scenes and emotional moments.