A crossover with the Avengers could also be cool. The Sailor Scouts could team up with the Avengers to fight a common enemy. Picture Sailor Moon using her healing powers on an injured Iron Man or Sailor Mars using her fire powers alongside Thor. Their different powers and fighting styles would make for an exciting combination.
One idea could be a crossover with the Harry Potter universe. Sailor Moon and her friends could attend Hogwarts and have to deal with both magical threats from the wizarding world and the dark forces they usually face. For example, they might help the students at Hogwarts fight off a new kind of dark magic that has similarities to the dark energy they combat in their own world.
Another possibility is a crossover with the Pokémon world. The Sailor Scouts could travel to the Pokémon regions and form bonds with Pokémon. Maybe they would use the Pokémon's powers in addition to their own to battle against an evil organization that is trying to take over both the Pokémon world and the world they come from.
One idea could be that the Sailor Scouts somehow end up in the SVTFOE universe. They could team up with Star and Marco to fight a common enemy. Maybe an evil force that combines the darkness from both universes.
Well, a cool plot might be that the Dragon Balls are stolen by an evil force from the Sailor Moon universe. So, the Z Fighters have to travel to that universe to retrieve them. Along the way, they meet the Sailor Scouts and realize they need to work together. The Sailor Scouts could also learn about the power of the Dragon Balls and how they can be used for good. They might even help the Z Fighters in their search by using their unique powers to track down the stolen balls.
Maybe there could be a dark force that is threatening both the Inuyasha world and the Sailor Moon world. So, Sailor Moon and her Sailor Guardians team up with Inuyasha, Kagome, and the others. They could combine their powers in unique ways. For example, Sailor Moon's healing powers could be used on Inuyasha when he gets seriously injured in a fight against the common enemy, and Inuyasha's strength could be used to protect the Sailor Guardians from some of the more physical threats in his world.
One idea could be that the Soul Reapers in Bleach are somehow affected by the magic in the Sailor Moon universe. For example, their zanpakuto (swords) start to gain new powers related to Sailor Moon's elemental powers like fire or water. Another plot could involve a character from Sailor Moon, say Sailor Mercury, using her intelligence to help the Bleach characters understand a new and dangerous threat that has elements of both universes. Maybe she could analyze some strange energy that is a combination of Hollows and the Dark Kingdom's power.
One interesting plot idea could be that Natsu, being a powerful fire mage, somehow gets transported to the Sailor Moon universe. He could team up with Sailor Mars, since they both have an affinity with fire. They might face a new enemy that is immune to normal attacks but is vulnerable to the combination of Natsu's dragon - slaying magic and Sailor Mars' spiritual powers.
One idea could be that the Sailor Scouts are transported to the Digital World. They team up with their respective Digimon partners based on their powers. For example, Sailor Moon could be paired with a Digimon that has lunar - related powers. They then have to fight a new enemy that threatens both the Digital World and the Earth.
One idea could be that Ranma somehow gets involved in the fight against the Dark Kingdom in the Sailor Moon universe. Maybe his curse could be related to the magic there. For example, his female form could be mistaken for a new Sailor Scout by the bad guys.
A possible plot is that a powerful dark entity is causing chaos in both the Sailor Moon and Twilight worlds simultaneously. The Sailor Scouts and the Twilight vampires and werewolves have to form an uneasy alliance. Sailor Mercury could use her intelligence to analyze the new enemy's weaknesses. Jacob might teach the Scouts some of his wolf - pack fighting tactics. The story could explore how the two very different groups overcome their differences and work together to save both of their worlds.
One idea could be that Ranma accidentally stumbles into the world of Sailor Moon. Maybe he gets caught up in a fight against a youma and the Sailor Scouts mistake him for an enemy at first. But then they realize he has his own unique fighting skills and they team up to defeat the common foe.
Another interesting concept is a love triangle. Suppose Ranma falls for Sailor Moon, but Tuxedo Mask is already in the picture. This could lead to a lot of comical and tense situations. Ranma might try to outdo Tuxedo Mask in protecting Sailor Moon, leading to some friendly rivalry. Also, his curse could add an extra layer of complication. What if he turns into a girl when he's around Sailor Moon at an inconvenient time?