Perhaps Usagi gets sent to an alternate dimension where the concept of harems is the norm. There, she has to navigate her relationships with different characters who all vie for her attention, while still trying to find a way back home and fulfill her duties as Sailor Moon.
One idea could be that Usagi, being the kind-hearted leader she is, gradually forms a harem of characters who are drawn to her pure heart and strong sense of justice. For example, the various Sailor Scouts could develop deeper feelings for her beyond just friendship, leading to a complex web of relationships.
Tuxedo Mask could also be in the harem. He has a long - standing relationship with Usagi, and in a harem scenario, his feelings for her could be even more intense, competing with others for her love.
One idea could be that Naruto somehow gets transported to the Sailor Moon universe. In this new world, the Sailor Scouts initially see him as an oddity but gradually come to respect his ninja skills. As for the harem aspect, Naruto's kind heart and unique abilities attract the Scouts, leading to a series of adventures where they all have to work together to protect both their worlds from a common threat. Maybe a new villain emerges who combines the dark jutsu of Naruto's world and the dark magic from the Sailor Moon world.
Well, perhaps Naruto has a special power that is needed to save both his world and the Sailor Moon world. As a result, the female characters from both Naruto and Sailor Moon start to develop feelings for him. For example, Sailor Moon might be drawn to his never - give - up attitude, while Sakura from Naruto could see a new side of him in this strange new setting.
One idea could be that the OC is a new senshi from a far - off planet who arrives on Earth just as a new threat emerges. The Sailor Scouts are initially suspicious but soon realize they need all the help they can get.
One interesting plot idea could be a time - travel scenario where Sailor Moon goes back in time to prevent a major event that led to the rise of a powerful enemy. Another could be a crossover with another popular anime, like having Sailor Moon meet Naruto and they team up to fight a new threat.
Love and loyalty are also big themes. The Sailor Senshi are extremely loyal to Usagi, and there are often undertones of platonic love in their relationships. They would sacrifice a great deal for her, and this is explored in many different ways in various fanfictions, like one where a Senshi risks her life to save Usagi from a powerful dark force.
Well, in Sailor Moon dark fanfiction, a cool plot could be the Sailor Guardians facing an enemy that can manipulate their worst fears. This would make them question their own abilities and loyalties. Also, a story where the power source of the Sailor Guardians is somehow tainted, turning their powers dark and making them struggle to control it. Or perhaps a plot where a new dark Sailor Guardian emerges, with powers equal to or greater than Sailor Moon's, causing chaos in the magical world.
One idea could be that the characters from RWBY end up in the Sailor Moon universe and have to learn the ways of the Sailor Scouts. For example, Ruby could be intrigued by Sailor Moon's transformation and try to adapt her Crescent Rose to work in that magical world.
An interesting plot could be that Goku and Sailor Moon meet during a multiverse tournament where representatives from different anime universes are competing. They initially don't get along because of their different fighting styles and beliefs, but as the tournament progresses, they realize they can learn from each other. Together, they face off against a cheating opponent who is using unfair tactics to win. Through their combined efforts, they not only defeat the opponent but also learn to respect each other's worlds and ways of fighting.
Well, perhaps it could be a story where Beryl is cursed and Usagi has to find a way to break the curse. Usagi, with her compassion, feels that she can't just leave Beryl in this state. She embarks on a journey, using her Sailor Moon powers and the help of her friends. Along the way, she discovers more about Beryl's past and the reasons behind the curse. This knowledge helps her to finally break the curse, and in the end, Beryl is so grateful that she becomes an unexpected ally to Usagi and the Sailor Guardians.