One interesting idea could be Naruto coming back with new and enhanced jutsu. Maybe he returns with a power that combines all the elements in a unique way.
One idea could be that the resurrected alien has some new powers. Maybe it can now blend into its surroundings like a chameleon, which adds a new level of danger. Another could be that the alien forms an alliance with a group of humans who are outcasts from society, and together they try to take over a powerful corporation.
One idea could be Ichigo having to face new and more powerful enemies in his resurrected form. Maybe he discovers new powers that come with this resurrection and has to learn to control them quickly to save his friends.
Perhaps a character who was thought to be dead returns with a new mission and tries to recruit the Young Justice team for a greater cause. This could lead to internal conflicts within the group as they decide whether to trust this new/old ally.
One interesting plot idea could be that Reiri and Riza have to team up to save the princess from a powerful dark force. They might face various challenges along the way, like difficult magical barriers or dangerous monsters. Another idea is that there's a misunderstanding between them at first, but as they work together, they come to understand and respect each other more. Maybe they also discover a hidden power within themselves or a long - lost secret about the princess that helps in their quest.
One idea could be that Hime and Hiro have to face a powerful new enemy together. They might discover a hidden power within their relationship that helps them defeat the foe. For example, a new type of magic that only activates when they hold hands or something like that.
One interesting idea could be the combination of Naruto's ninja skills with mecha technology. For example, Naruto might use his chakra to power up the mecha in unique ways. Another idea could be the new enemies that are created specifically for this mecha - Naruto concept, like robotic shinobi that require different combat strategies compared to normal foes. Also, the design of the mecha Naruto itself can be really cool, perhaps with features inspired by the Nine - Tails.
Maybe in the fanfic, the Resurrection Stone was never truly lost. It was secretly being protected by a group of centaurs in the Forbidden Forest. A young Hogwarts student stumbles upon this secret while exploring the forest. The centaurs test the student to see if they are worthy of handling the stone. If they pass, they are given the stone to use for a short time, but they must return it unharmed. This could lead to a series of adventures as the student tries to decide who to bring back, if anyone.
Another idea is that Aizen somehow ends up in the Naruto universe during the time of the Fourth Great Ninja War. He could try to manipulate both sides for his own gain. But Naruto, with his ability to see the good in people, might try to reason with Aizen and show him a different path. It could be a story of redemption or a great battle if Aizen refuses.
In a 'Naruto Mermaid Fanfiction', the mermaids could be in danger from an evil organization that wants to capture them for their precious scales. Naruto teams up with a mermaid princess to stop this threat and in the process, they learn about each other's worlds.
One idea could be a crossover where Naruto and Pucca end up in the same world due to a strange ninja jutsu gone wrong. Naruto is confused by Pucca's constant chasing of Garu, and he tries to help Garu escape in his own Naruto - style way.