A Gilligan's Island and 'Star Trek' crossover would be cool. The Starfleet crew could beam down to the island by accident. They might try to help the islanders with their advanced technology. Captain Kirk could befriend the Skipper, and Spock could have some really interesting interactions with the Professor as they both are very logical thinkers. Uhura could use her communication skills to try and get a signal out for rescue, which is something the Gilligan's Island crew has been trying to do for ages.
One idea could be a crossover with 'Lost'. The survivors of the 'Lost' plane crash end up on Gilligan's Island. They could interact with the Gilligan's Island cast, share survival skills, and there could be a clash of cultures. For example, Sawyer's con - man ways might be at odds with the simple - mindedness of Gilligan. Another plot could be a crossover with 'Jurassic Park'. Dinosaurs somehow end up on the island. The Gilligan's Island gang has to figure out how to deal with these prehistoric beasts while still trying to get rescued. Maybe the Professor uses his scientific knowledge to try and find a way to co - exist or get rid of the dinosaurs.
One idea could be that a mysterious ship arrives on the island, but it turns out to be a time - traveling vessel. The castaways have to decide whether to take the risk and go with it to a different era. Another could be that Gilligan discovers a hidden cave filled with strange artifacts that seem to have magical powers. They could then use these powers to try and finally get off the island.
Combining Ginger with Sherlock Holmes would be a great match. Ginger is used to using her charm and wits to get what she wants, and Sherlock Holmes' deductive skills are unrivaled. Holmes could help solve some of the mysteries on the island, like why they keep getting so unlucky with rescue attempts, while Ginger could use her charm to help Holmes interact with the other islanders in a more social way.
One interesting story could be about how they built their shelters. They had to use the natural resources on the island like palm fronds and bamboo to create makeshift huts to protect themselves from the elements.
One idea could be a crossover with another popular animated show like 'Adventure Time'. Finn and Jake could end up on Total Drama Island and compete in the challenges. It would be hilarious to see their different personalities interact with the Total Drama characters.
In a 'naruto on island fanfiction', Naruto might find himself on an island that is constantly changing its geography due to some sort of powerful and unstable ninjutsu. This would force him to constantly adapt and use his ninja skills in new ways. He could also meet a spirit or entity on the island that claims to know his destiny and he has to decide whether to trust it or not. There could be a race of people on the island who are immune to normal ninja attacks and Naruto has to learn their ways to be able to defend himself and communicate with them.
Maybe a crossover with a magical anime. The nanbaka characters could suddenly find themselves in a world full of magic. Some of the nanbaka characters might be really good at using magic in unexpected ways, like Jyugo using his shackles in a magical battle.
A crossover with a modern - day action story could be really cool too. Spartacus and his crew could be brought to the present day through some time - travel mishap. They then have to navigate the modern world, learning about new weapons and technology. They could use their ancient fighting techniques in modern combat situations, like taking on a powerful criminal organization.
Maybe in the fanfiction, the three - tailed beast crosses over into a modern - day human world. People initially fear it, but then they discover that it has a gentle side and is actually trying to find its way back home. It could form a bond with a group of humans who help it on its journey, leading to many adventures along the way.
One idea could be a crossover with 'Fullmetal Alchemist'. Dorohedoro's dark and gritty world combined with the alchemical concepts would be fascinating. For example, the characters from Dorohedoro could be exposed to the laws of equivalent exchange. Another plot could involve a crossover with 'Hunter x Hunter'. The nen abilities in 'Hunter x Hunter' could interact in strange ways with the magic in Dorohedoro's world. Maybe a character from Dorohedoro has to participate in the Hunter Exam. A third idea is a crossover with 'Tokyo Ghoul'. The idea of the ghouls' existence in Dorohedoro's setting and how they would coexist or clash with the existing creatures and characters there.
One idea could be a Vegito crossover with the Dragon Ball GT universe. Vegito could face off against the Shadow Dragons, creating an epic battle of power. Another could be a crossover with the One Piece world, where Vegito has to navigate the Grand Line and deal with pirates. Maybe he teams up with the Straw Hats to take on a common enemy.