• Chibi Usa travels into a parallel timeline, either in 20th Century Tokyo or Crystal Tokyo
• Exploring the lives of the sailor soldiers who were subjugated by Galaxia
• Sailor Chibi Moon begins leading her sailor team, prior to the events in Stars when she returns to the past to assist Sailor Moon

Would it be possible to do a 'Pick Your Own Adventure' style of RP?

I am guessing there would still be a central story, but at regular intervals the characters/role-players would have to decide to pick one of two options. I assume there are pick your own adventure generators on the Internet that could help with this idea.

Halloween-themed: Characters wake up as ghosts, suddenly haunting a mansion, but they don't remember how they turned into ghosts

The demon Mujaki traps everyone in their dreams within their best fantasies, but those best fantasies slowly turn into nightmares. Mujaki is enchanted by Chibi-Usa's beautiful dream and decides he wants to spend the rest of eternity with her. Helios has to save everyone from their nightmares, so they can all gang up and save Chibi-Usa from Mujaki. Inspired by the Urusei Yatsura movie 'Beautiful Dreamers.'

An RP event where we have to use a word generator and include all the words it generates in our posts.

https://randomwordgenerator.com/

How about a casual event where everything is from the civilians point of view? So it would feature Usagi's parents, friends, etc. Could be a fun little place to feature characters that we wish we knew more about.

A casual event using only old OCs. You have to take an OC from childhood/a long time ago and finally flesh them out or tweak them a bit to make them work (if needed) and rp them.