It could be a jealous rival cheerleader who has made a deal with a dark entity. This rival is envious of the main character's popularity and success in cheerleading. The dark entity gives her powers to create chaos during cheerleading events and tries to harm the protagonist. So, this corrupted rival cheerleader becomes the main antagonist.
One possible plot could be that a cheerleader discovers she has Sailor Moon - like powers. For example, she could be at a big cheerleading competition when suddenly strange things start to happen. She realizes she can use her pom - poms as a sort of weapon or tool, just like Sailor Moon's wand. Maybe she has to fight off some dark forces that are trying to disrupt the event, all while still maintaining her cheerleading duties and trying not to expose her new powers to her teammates.
A corrupted spirit that was once a guardian of the Underworld but has been twisted by jealousy or a thirst for power. This spirit sees the Sailor Guardians as a threat to its newfound plans of domination. It uses its knowledge of both the Underworld and the weaknesses of the Sailor Guardians to try and defeat them. It might also try to turn some of the underworld creatures against the Sailor Guardians.
The Dark King from Sailor Moon could team up with the Volturi. The Dark King's thirst for power combined with the Volturi's strict vampire laws could create a really menacing force. They could be trying to take over both the magical world of Sailor Moon and the vampire - filled Twilight world.
Maybe a corrupted version of one of the Sailor Scouts. She could be jealous of Naruto's attention towards the other Scouts in the harem. So, she makes a deal with a dark force from Naruto's world, like a powerful Orochimaru - like character. This combined power of dark jutsu and a twisted Sailor power would create a very interesting and complex main antagonist for this crossover fanfiction.
Typically, Sailor Moon herself would be one of the main characters. In a fanfic like this, she might be at the center of the story, dealing with the events related to Andromeda Rising. Her friends, the other Sailor Scouts such as Sailor Mercury, Sailor Mars, etc., would also likely be main characters as they usually support Sailor Moon in any adventure. There could also be new characters introduced specifically for this fanfic that are related to the Andromeda Rising concept.
It could be an evil sorcerer who has the power to steal chakra and magical energy. He plans to use this stolen power to reshape both the Naruto and Sailor Moon universes according to his own dark desires. He's able to create powerful illusions that fool even the most experienced ninja and senshi, making him a very difficult enemy to face.
A new character could be created as the main villain. This villain could be a powerful sorcerer who has studied the magics of both Sailor Moon and SVTFOE. He discovers a way to merge the two universes in a way that benefits him but is harmful to everyone else. He might try to control the Sailor Crystals and the magic of SVTFOE at the same time. To stop him, the characters from both universes would have to put aside their differences and fight together.
The main characters are Usagi Tsukino / Sailor Moon, Ami Mizuno / Sailor Mercury, Rei Hino / Sailor Mars, Makoto Kino / Sailor Jupiter, and Minako Aino / Sailor Venus. Also, Tuxedo Mask plays a crucial role.
In a Sailor Moon fanfic, coffee might be significant in terms of character development. If a character is shown to be addicted to coffee, it could be a sign of their stress levels due to their battles and responsibilities. It could also be used to bring a sense of normalcy to the story. The Sailor Moon universe is filled with magic and danger, and coffee can be that ordinary thing that grounds the characters and the readers. Additionally, coffee could be used to mark a change in a character's life. For instance, if a character starts drinking coffee after a particularly difficult battle, it could signify their new - found maturity or a different approach to dealing with their challenges.
It could be a dark sorcerer who wants to steal the power of the moon for his own evil purposes. He sees Mune as the only obstacle in his way, so he tries to undermine Mune at every turn.