Setting
This RPG is set in our world in Tokyo, Japan, Azabu Juuban district. This means that all the landmarks included in Sailor Moon are also in our story, including the Hikawa Shrine and Juuban High School. It is a modern-day RPG, so everything we have, they have. Keep Juuban in mind when writing for your character; for instance, the current Sailor Psi goes to college at Temple University Japan, which is located there. Also keep in mind that this RPG is based mostly on the manga with a few tiny influences from the anime; remember, Takeuchi wrote the MANGA, not the ANIME.
Tau Ceti
The Tau Ceti Star System is another dimension, but it is very different from the Negaverse and the Universe. It is the original home of the Death Busters, the five higher-ups in the Tau Ceti military that now reside in our Universe to begin invading. There is only one planet in Tau Ceti, and its people once believed in the values of silence and meditation. The people on Tau Ceti do not speak; they communicate through simple gestures similar to our own sign language. Their culture is very much one of restrained mannerisms and meditation. Rather, it was like this, before Pharoah 90 (an incarnation of Chaos) took over and turned the planet's government into a militaristic dictatorship.
About half a century ago, the royal family of Tau Ceti was deposed by Pharoah 90 and the culture became much more violent and military-based, though silence and meditation were still valued (more for their battle potential than before). Pharoah 90 ordered the people of Tau Ceti to attack other dimensions so they could be absorbed into Pharoah 90. Most of the people did not want this to happen, but Pharoah 90 forced them to attack (among other dimensions) the Negaverse. Eventually, Pharoah 90 was destroyed when Chaos was dispersed into the hearts of all men at the end of the Galaxia arc, but Lucifer, who was once Pharoah 90's third-in-command (next to Mistress 9), had grown insane because of his lover's death, and still wants to invade other dimensions because he believes it was his lover's last wish. He is now invading the Universe, saving the Negaverse for later because he believes it has senshi while the Universe does not (remember, no one knows about the Crisis Senshi but the Negaverse Senshi).
Now, the Tau Ceti Star System is under a new generation of rulers that were raised with Pharoah 90's ideals, which is why they want to silence other dimensions. However, this does not mean that a Witch will definitely agree with those ideals, but she will most likely at least accept them and go along with them for power or something else. The newer generation follows Lucifer's rule, and in general they believe what they are doing is right. Think of it almost in a "White Man's Burden" way. The Witches will probably experience some sort of culture shock as the result of being exposed to our world, which has a very different culture from Planet Tau. Maybe they love our culture? Maybe they hate it? It's up to the applicants.
Negaverse
While most of the RPG will be set in our "Universe," some action may occur in the "Negaverse" where Sailor Moon and her senshi team are from. This realm parallels our own, and Sailor Moon and her friends are from the Negaverse equivalent of our Tokyo. The one difference between the two realms is that the Negaverse has Sailor Senshi while the Universe (until very recently) doesn't. To understand why our world is the only realm that does not have Sailor Senshi (and it is), one must first understand the nature of Mana, the life-blood of existence.
On Time: One month of Negaverse time is equal to one year in our own realm. This explains how Sailor Moon was able to send Takeuchi the message about what would happen in 15 years and remain relatively the same age (a year and three months older) later. The Negaverse runs by a 12 month calendar much like America. This isn't really that big of a deal, it's just meant to explain the time gap between Takeuchi's prophecy and the sailor senshis' adventures without making the Negaverse Senshi 15 years older.
On the Prophecy: Naoko Takeuchi received the prophecy from the Moon Princess of the present time. Confused? Here's what went down; 15 Universe years ago, or 1 year and 3 months ago in the Negaverse, the sailor senshi started their adventures (aka the beginning of the Dark Kingdom arc). The present Moon Princess went back in time with Sailor Pluto to warn Naoko Takeuchi about it 15 Universe years in the past, so that the Crisis Senshi could train between the beginning of the Negaverse Senshis' battles and now. However, Takeuchi didn't listen to the prophecy (as we all know). Make sense? GOOD.
Mana
Long ago, Mana was born. No one really knows how this pure white liquid was formed or why, but Mana naturally flows through existence in a fairly random manner. When a great deal of Mana clusters together at one point, the core of a realm is created, the Mana solidifies, and the realm is born. From this Mana, the basis of life is born, and that evolves into several different species including human beings.
While all human beings have Mana within their blood, a select few have more than others; these few are the Sailor Senshi that are destined to protect their realms. Although Sailor Senshi were originally people with extra abilities, like extra strength or purer hearts, eventually the humans in each realm were able to create technology that could manifest the true potential in this Mana; henshin sticks. With these tools, the humans with more Mana than others were able to manifest their Mana into a physical form (Sailor fuku) that allowed them greater powers.
Why doesn't our realm have Sailor Senshi? The answer is both extremely simple and extremely complicated. Our realm is located within very close proximity to the "pocket realm," which is at the center of existence and which is where the souls of the Crisis Senshi were born. In reaction to the pocket realm, our Universe's Mana core created a large bubble shield around itself. However, by expending its extra Mana in this way, the core was only able to create a planet, and was unable to distribute any more Mana to human beings for them to become Sailor Senshi.
With this in mind, and with the fact that the Universe was so close to the pocket realm, the guardians of the Crisis Senshi decided to allow this realm to exist without Sailor Senshi; the bubble shield created by the Mana core would be enough to protect the realm from any real dangers that the humans could not handle themselves.
However, something strange has occurred recently; a hole has formed in the bubble shield, and no one can fathom why. Some suspect that the new enemy has something to do with it – others can only speculate. Either way, with this in mind, the Crisis Senshi have been awakened.
Villains
So where do the villains live? Each faction of villains presides in a base somewhere in the Universe; the Black Moon Clan on Nemesis, the Death Busters in Tokyo, Japan, and the Dark Kingdom in the North Pole. Remember also that all of the villains are able to teleport to Tokyo, where they have taken up lives as citizens to disguise themselves in the hopes of operating incognito.