Why do they wear sailor suits?
The sailor suit is a common school uniform in Japan and is widely associated with junior high school girls.
Why is Rei's daily outfit different and why does she have extra powers?
Rei works at her grandfather's Shinto temple as a sort of apprentice. At the temple, she wears the traditional temple costume. The position she is training for is miko, a female "exorcist" and we have seen her use her seals ("Fire bombs") to banish evil spirits. The writing on the seal says "Akuryotaisan" which translates "evil spirits run away". These seals are called ofuda and in Japanese tradition they are able to trap the power of spirits. "Miko" can also mean an intermediary between the supernatural and human worlds (e.g. "Suzako no Miko" in Fushigi Yuugi).
The monsters that the girls fight are called youma in Japanese.
As for the grey outfit, Rei goes to T.A. Private Girls School, whereas Serena, Amy and Lita go to Juuban Jr High School.
What about Lita's brown uniform?
In the Japanese version, Lita's height is a big deal. Juuban Jr. High didn't have any uniforms that would fit her, so she still wears her former school's uniform.
Why does Darien call Serena "meatball head"?
This is a pretty accurate english equivalent to the japanese joke. He calls her odanga atama, the name of a dessert which looks like little rolled up balls, a reference to Serena's hairstyle.
What is that red building that looks like the Eiffel Tower?
It's the Tokyo Tower, a prominent landmark of the Tokyo skyline.
What is the Negaforce?
Queen Beryl repeatedly refers to the need for energy in order to release the destructive power of the Negaforce. We sometimes see her consulting this force for guidance. In the original version, the villians are trying to gather energy to reincarnate their empress Queen Metalia and this is who Beryl sometimes speaks with.
What is the relation between Sailor Venus and Sailor V?
They are the same person. Artemis found Mina before Luna found Serena, and she acted as Sailor V until Artemis and Luna got all five girls together, at which point she became Sailor Venus (orange skirt instead of blue and without the pink mask.
In real life, the "Sailor V" comic book series was the first sailor-suited superheroine comic created by Ms. Naoko Takeuchi and when she created "Sailor Moon", a longer, more complex story based on the Sailor V idea, she decided to incorporate her old character into the new series.
How old are the girls?
At the beginning of the first series, they are all supposed to be 14. Here are their birthdays:
Serena -- June 30 -- Cancer
Amy -- September 10 -- Virgo
Raye -- April 17 -- Aries
Lita -- December 5 -- Sagittarius
Mina -- October 22 -- Libra
Rini -- June 30 -- Cancer
Darien -- August 3
By cosmic coincidence, if you look up the signs of the Zodiac, you will find that Cancer is ruled by the moon, Virgo is ruled by Mercury...etc.
Is there really a Sailor Uranus?
Yes. Later episodes, not available in english, introduce:
Character -- Japanese Name -- Birthday
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Sailor Saturn -- Tomoe Hotaru -- January 6
Sailor Uranus -- Tenoh Haruka -- January 27
Sailor Neptune -- Kaioh Michiru -- March 6
Sailor Pluto -- Meioh Setsuna -- October 29
If you're getting confused about name order, their given names are Hotaru, Haruka, Michiru and Setsuna. In the English fan-dub, their names are Victoria, Erica, Michelle and Susan. I have heard that the names on the dolls that are sold in North America of Sailor Uranus, Sailor Neptune and Sailor Pluto are Corrin, Nerissa and Celia, respectively.
Why is there no Sailor Earth?
Darien's Japanese name is Chiba Mamoru. Mamoru means "protector", chi means "Earth", and Tuxedo Mask is the hero from Earth.