Well, in 'naruto excalibur fanfiction', a cool concept might be the different forms of Excalibur. It could be like in Naruto where there are different levels of jutsu. So perhaps there are different forms of Excalibur that can be unlocked depending on the character's growth or the situation. And the characters from Naruto would have to figure out how to master these forms.
In this type of fanfiction, the idea of the Excalibur's origin could be reimagined in the context of the Naruto universe. It could be tied to some ancient ninja clan or a powerful sage. And the characters in Naruto might have to go on a quest to discover the true nature of Excalibur, facing many challenges along the way that are a blend of Naruto - style battles and Arthurian - style quests.
One interesting concept could be a new power - up for Sonic. In Dark Excalibur Sonic fanfiction, perhaps Sonic discovers a dark - themed power that is related to the Excalibur. This power could change his appearance and abilities, making him look more like a 'dark hero'.
One interesting concept could be an exploration of Naruto's dark side. It might show how his experiences could have turned him truly evil, like if he had been more influenced by the hatred in the ninja world from the start. Maybe in this fanfiction, he uses his powers for self - gain rather than for the good of the village.
In 'naruto dark naruto fanfiction', the concept of Naruto's doppelganger or 'dark Naruto' is often explored. This could be a manifestation of his repressed negative emotions. It might be that this dark Naruto has its own goals that are contrary to the real Naruto's. For instance, it could want to destroy the Hidden Leaf Village instead of protecting it. And the story could revolve around how Naruto deals with this inner darkness, either by trying to suppress it or, in a more extreme version, merging with it and becoming a different kind of hero or anti - hero.
In Naruto fanfiction, the Sharingan is often explored in unique ways. For example, some fanfictions might expand on its ability to not only copy jutsu but also to predict an opponent's moves on a whole new level. Another interesting bloodline concept could be the Uzumaki's massive chakra reserves, and fanfictions may play with how this could be used in different scenarios, like creating entirely new jutsu.
Some fanfictions might explore the idea of Naruto befriending an Espada. This friendship could lead to Naruto learning about different ways of combat and power management from the Espada. It could also result in the Espada having a change of heart due to Naruto's positive influence, and together they could face new threats in the Naruto universe that neither could face alone.
One interesting concept could be alternate character developments. For example, a fanfic might explore what would happen if Naruto had a different approach to his training from the start. Another concept could be unique jutsu combinations that are not in the original series. Also, exploring different relationships between characters in new scenarios is quite common, like how Naruto and Sasuke's friendship could have evolved in a more complex way due to different plot twists in the fanfiction.
One interesting concept could be the exploration of new jutsu through loopholes. For example, a character might discover a loophole in the chakra system and develop a unique jutsu based on that. Another could be loopholes in the ninja academy rules, leading to unexpected character development. Maybe a character uses a loophole to get special training or resources.
One interesting concept could be the new powers that characters gain due to the mutagen. For example, Naruto might develop some unique jutsu or physical abilities that are a result of the mutagen's influence. Another concept could be the altered relationships between characters. Maybe the mutagen causes some characters to be more distrustful or more united in a different way than in the original Naruto story.
One interesting concept could be Naruto with metal-based powers. For example, he might be able to manipulate metal in combat, like creating sharp metal shurikens out of thin air or using metal to enhance his physical attacks. Another concept could be a world where the Hidden Leaf Village has advanced metal - working techniques that Naruto learns and uses to his advantage. Also, there could be a plot where an enemy uses metal - based jutsu against Naruto, forcing him to find new ways to counter.
One interesting concept could be the combination of ninja abilities with mecha technology. For example, a mecha might be powered by chakra, allowing for unique combat capabilities. Another concept could be the use of Sharingan or Byakugan in the mecha's targeting systems. And some fanfictions might explore how different ninja clans interact with mecha, like the Uchiha's sharing their fire - style jutsu knowledge to enhance the mecha's weaponry.