One idea could be a character from Naruto ending up in the Descendants' world. For example, Naruto himself could be transported there. He might use his ninja skills to deal with the challenges in the Descendants' world, like facing off against the villains in a very different way compared to the Descendants' characters. Maybe he'd use his shadow clone jutsu to confuse the bad guys or his Rasengan to take on powerful foes.
Another plot could involve a Descendants character coming to the Naruto world. Mal could arrive in Konoha. She would find the ninja world full of new and strange powers. Her magic would be a novelty there, but she'd also have to learn to deal with the more combat - oriented nature of the Naruto world. She could form an alliance with some of the ninja clans or perhaps even start a rivalry with some of the more headstrong ninja.
A more complex plot could be that there is a mix - up of magic and chakra. The Descendants' magic starts to seep into the Naruto world and vice versa. This causes chaos as ninja start to develop magical abilities and the Descendants' characters start to gain some ninja - like powers. Naruto and his friends have to work with the Descendants' crew to find a way to reverse this before both worlds are destroyed.
One idea could be a crossover with the 'Dragon Ball' universe. Naruto's descendants could team up with Goku's family to fight a common enemy. Another could be a crossover with 'One Piece', where they sail the Grand Line together in search of a powerful treasure that could change both their worlds. Or perhaps a crossover with 'Bleach', and they battle Hollows and Soul Reapers together in the afterlife.
One idea could be that the characters from Descendants end up in the world of Jessie by some magical mishap. Mal could use her magic to help Jessie deal with some of the difficult kids she babysits, like when they get into trouble at school. Another plot could be that the kids from Jessie visit the Isle of the Lost out of curiosity and try to bring some positive change there. Maybe they start a music club or something similar to engage the villain kids in a more positive activity.
One idea could be that a character from 'Once Upon a Time' (OUAT) accidentally travels to the world of 'Descendants'. For example, Emma Swan could end up there and have to deal with the different rules and characters. Maybe she tries to help some of the 'villain kids' in 'Descendants' to see that they don't have to follow in their parents' footsteps, just like she often helped people in OUAT find their true selves.
One idea could be that the demigods from Percy Jackson's world accidentally end up in the Descendants' universe. They could team up with the VKs (Villain Kids) to face a common threat that is related to both Greek mythology and the magic in the Descendants world. For example, an ancient Greek monster that has been awakened by the dark magic in the Isle of the Lost.
One idea could be a story where the characters from 'Descendants' end up in the 'Twilight' world. For example, Mal could meet Bella and they could form an unlikely friendship. Mal might be intrigued by Bella's relationship with Edward and the whole vampire - human dynamic in the 'Twilight' world.
One interesting plot idea could be a crossover where Naruto's senjutsu abilities are combined with another universe's magic system. For example, if he were to cross over into the Harry Potter universe, he could use senjutsu to enhance his magic or even teach the wizards about chakra. Another idea is a crossover with the Dragon Ball universe, where Naruto's senjutsu clashes with the ki energy of the Saiyans. Maybe he has to use senjutsu to face off against a powerful Saiyan who has come to the Naruto world. Or a crossover with the Bleach universe, and Naruto uses senjutsu to interact with the spiritual energy there, perhaps even helping Ichigo in a battle against a powerful Hollow by using his unique senjutsu skills.
One plot idea could be that Naruto characters end up in Ikebukuro. For example, Naruto himself could be searching for a new type of ninja tool that he heard can only be found in Ikebukuro. Meanwhile, the gangs in Durarara start to notice this strange, orange - clad boy with strange powers. Another idea is a character swap where some of the Durarara characters gain ninja abilities and get involved in Naruto - style battles in their own world. Maybe Celty could use her shadow powers in a more ninja - like way, like stealth and quick attacks.
One idea could be that Naruto characters are transported into the Splatoon world. They might initially be confused by the ink-based battles and the unique species. For example, Naruto could mistake an Inkling for a strange ninja from another land and challenge them to a friendly spar, only to find out about the ink shooting mechanism. Another plot could involve the Akatsuki from Naruto trying to steal the valuable ink resources in the Splatoon world for their own purposes. They would face off against the Splatoon heroes who are determined to protect their world's resources.
A cool plot could be that there's a tournament across different anime worlds, and Inuyasha and Naruto are chosen to represent their respective worlds. Along the way, they discover similarities in their pasts, like both having some form of demon - related heritage (Naruto with the Nine - Tails and Inuyasha being a half - demon). They also exchange combat techniques. Naruto teaches Inuyasha how to better use chakra control in his attacks, and Inuyasha shows Naruto some unique sword - fighting skills.
One interesting plot idea could be that Kaguya is reborn in the modern Naruto world. She has no memories of her past at first. Naruto discovers her and senses a strange power within her. As she starts to regain her memories, she struggles between her old self and the new world she's in. Naruto has to decide whether to trust her or not.