Another aspect could be his relationships. For example, his crew might be more distrustful of this darker Luffy at first. They are used to his positive and carefree self, so seeing a darker side could strain their bonds until they understand his new motives. Also, his relationship with the other pirates and the World Government could be completely different, perhaps more antagonistic and less about the fun adventure.
One possible interesting concept could be the re - imagining of Luffy's adventures with a female perspective. It might explore how a female Luffy would handle the challenges differently. For example, in the original story, Luffy's straightforward and fearless nature is a big part of his charm. A female Luffy in fanfiction could bring a new dimension to that, perhaps showing more emotional depth in certain situations while still maintaining that boldness. Another concept could be different relationships. In the original, Luffy has strong bonds with his crewmates. A female Luffy might have different dynamics in those relationships, like different types of friendships or rivalries that add new layers to the story.
One interesting concept could be a darker version of Luffy's leadership. Instead of his usual carefree and positive leadership, it might show a more calculating and perhaps even ruthless side in making decisions for the crew's survival in extremely tough situations.
One interesting concept could be Luffy having to deal with the corrupting influence of the Dark Dark Fruit. Maybe he struggles to maintain his usual carefree and positive attitude while using its powers. For example, the power might make him more withdrawn at first as he tries to figure out how to control it without losing his sense of self.
One interesting concept is the idea of the One Piece characters facing the challenges of the Dark Souls world. For example, Luffy trying to defeat the bosses in Dark Souls with his rubber powers. It's a really cool mix of the two different power systems.
One interesting concept is alternate universe stories. For example, what if Luffy didn't eat the Gum - Gum Fruit but a different Devil Fruit? Another concept could be character backstories that are expanded or changed. Maybe a fanfic delves deeper into Sanji's time at the Baratie and creates new relationships or events during that period. Also, there are fanfictions that explore different power - up scenarios for the characters, like if Zoro found a new type of sword with unique abilities.
Often, in fanfiction about Power Dark Luffy, the story might deviate significantly from the original One Piece plot. Writers may explore different power-ups for him. His new 'dark' powers could be related to shadow manipulation or some sort of dark energy. This not only changes his appearance but also his fighting style. His relationships with other characters in the One Piece universe would also be affected, leading to new and exciting storylines.
One interesting concept is a crossover with other popular anime like Naruto. Imagine Luffy and Naruto teaming up, it would be a clash of two very different power systems and personalities. Another concept could be a crossover with a superhero universe. For example, Luffy meeting Superman. Their powers are so different, it would make for an exciting story.
In some One Piece gamer fanfiction, there's the concept of 'cheat codes'. These could be things like a secret knowledge that allows a character to instantly learn a new Haki technique or unlock a hidden island full of treasures. Also, the idea of character customization is popular. So, a fanfic might explore how Luffy could customize his straw hat or add new abilities to it, like making it a shield or a weapon enhancer.
In some One Piece marine fanfiction, there are concepts about marine - pirate alliances in secret. This goes against the normal narrative but creates a really interesting dynamic, as it makes you wonder about the possible reasons behind such alliances, like mutual benefits in a particular situation or a hidden agenda that might be beneficial for both parties in the long run.
One interesting concept could be the idea of Pokemon existing in the One Piece world. For example, trainers in the Straw Hat crew. Luffy might befriend a really strong and unique Pokemon, like a Pikachu with a Conqueror's Haki ability. It would add a whole new dynamic to their adventures as they explore the Grand Line.