Sailor Senshi

Sailor Senshi

Sailor Senshi/Sailor Guardians are female warriors who are incarnations of the planets themselves or people who are the descendants of the Roman or Greek Gods respectively. They wear sailor attire with unique colors representing the planets they are protected by. Each planet, depending on the mythos, represents an element, and granted to each guardian, are magical girls that protect the world from evil. Every guardian has a Sailor Crystal, where their power is held and in essence their soul/self.
Their power also consists of the ability to fly, telepathy, create shields, and teleportation to name a few.

Sailor Castles

Each planet holds a castle floating in the atmosphere that the guardians and people live in.

• Mirage castle on Mercury belongs to Ami Mizuno.
• Phobos and Deimos on Mars belong to Rei Hino.
• Io castle on Jupiter and belongs to Makoto Kino.
• Magellan castle on Venus belongs to Minako Aino.
• Miranda castle on Uranus belongs to Haruka Tenoh.
• Triton castle on Neptune belongs to Michiru Kaioh.
• Charon castle on Pluto and belongs to Setsuna Meioh.
• Titan castle on Saturn and belongs to Hotaru Tomoe.
• Silver Millennium on the moon in the past then on 30th century Earth belongs to Usagi and her daughter Chibiusa and Mamoru Chiba via marriage.
Mamoru Chiba was Prince Endymion in the past and ruled the Golden Kingdom in Elysion. He owns the Golden Crystal.

These castles also hold their power guardians, a mini representation of the guardians though I want to believe they just take on those forms and can turn into anything else if they want. These castles hold high-tech computers and when the 30th century arrives and the guardians ascend they will rule these places and still guard Usagi. A possibility is that humanity will continue to thrive and these are places, the castles, that will hold a load of people to be governed from earth (J's interpretation of events).

Origin Story

In the world of Sailor Moon, there was a place called Silver Millenmum where Queen Serenity was the ruler and gave birth to her daughter, Princess Serenity. It is unknown who her father is and is never mentioned. Princess Serenity was the only child of the queen and Serenity had four guardians of the closest planets as her aids, Mercury, Venus, Mars, and Jupiter respectively. They each were princesses of their planets and warriors.
They were protective and loving to the little princess and were known as the Inner Guardians. Ones like Pluto, Uranus, and Neptune, were on the outskirts doing their duty of protecting them from outside forces and are known as the Outer Guardians. Saturn was asleep as well and it was said if those three were ever in close contact their talismans would awaken Saturn from her slumber.

Power Scaling

Now you are asking, are they powerful? In terms of the 90s anime, they are capable and can deal with monsters, though it was Sailor Moon that did the final blow. There have been instances where a Senshi did the final blow to an enemy but rarely. In the manga and Crystal adaption, they are capable of destroying enemies with their attacks.
With Sailor Moon using her Silver Crystal, she pretty much becomes omnipotent and by mastering that power, the entire world in the 30th century is at peace and people are granted eternal life.
The 90s adaptation has a lot of enemies get redemption for some of the characters that need or deserve it, Beryl, Doom Phantom, Death Busters, Mistress 9, Nelhelania (rehabilitated later), and Galaxia (purified by Moon by getting rid of Chaos) were turned into moon dust.
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The suits and powers get stronger with each new season and arc to varying degrees and by season 4 (for the Inners) and season 5 (the outers) gain "Crystal power" and their "Super forms" with an upgraded attire of a heart brooch and star earrings. Unfortunately, none of the guardians can go into Eternal mode in the original 90s anime while Sailor Moon is granted that power-up. In the new series that adapts the manga and films, that is rectified where with each upgrade the phrases changed and gain Eternal in the movies. In Eternal mode, the guardians have star-shaped brooches, high-heeled boots, orb shoulder pads, star-shaped tiaras, and double-layered skirts with similar colors for each guardian.
Also in the manga and Crystal films, they can turn into their princess forms which is a big power boost as they are linked to their respective planets.
Tuxedo Mask has no real power in the 90s adaption except for using roses while in his manga and crystal adaption he is capable of firing a powerful blast of energy, that is on par with a Kamehameha. Also, the Golen Crystal grants him some power as well but is never put into use after he acquires it.

Chaos and Cosmos

A big plot point in the manga and films is Cosmos and Chaos, the physical embodiments of order and chaos. Sailor Cosmos is implied to either be the future form of Sailor Moon, or someone else entirely, as Naoko Takeuchi has stated in interviews. Though you can come to your own conclusion; J sticks with her being Sailor Moon in the far-flung future, where a sad event awaits. Sailor Cosmos guards the Galaxy Cauldron, the place of birth for all beings and where all return to when they die.
In the last arc of Sailor Moon, all the guardians die due to Sailor Galaxia, and Sailor Moon has to confront the tyrant guardian. It is here where Usagi learns the origins of the world and something she must do; destroy the cauldron with chaos in it to prevent its birth but at the cost of no heavenly beings being born anew (her friends and Mamoru) or to continue as it were with everyone being reset and returned to the proper point in time (J's interpretation).
Usagi decides to believe that she will embrace the good and the bad and if it's her fate to ascend to Cosmos one day, she will do so and continue to believe. This in turn causes everyone to be reborn and I (J writing this) believe they all returned to the time a little after Galaxia and they continued to the destined future even with some added nuance.
Chaos also is born from the cauldron as a karmic balance sadly and it is always fated to return. She will gain a human form and rage war on the entire universe. She has enough power to eradicate creation given her title so she's no one to trifle with.
Harmony and Chaos are one and the same and though there will always be conflict, there are ones in this world that will protect people and the earth from injustice, evil, and corruption, Sailor Moon and the Sailor Guardians.
Due to the chronology of the series of manga being released in the 90s and it being the 20th century at the time, Jeff will use the 21st century to match with the Crystal adaption of the series to keep it concise. For example, Chibiusa being from the 30th century will only travel to the 21st century and not the 20th one from the previous iteration.
Also, the future of the 30th century experienced a second ice age and was awakened by Usagi's Silver Crystal, granting the inhabitants of earth eternal life and she and her guardians only physically look around their early 20s. Even though that's the case, they can still get killed as it's not immortality they have, at least in J's way of thinking.