Fans of Sailor Moon know that creator Naoko Takeuchi took care to plan out a lot of details for her characters. The original manga didn't just give fans the broad strokes of the personalities of the characters, it also included things like blood types, birthdays, and zodiac signs.
Though the franchise might already have the zodiac signs (and in fact, those of the Sailor Senshi are those of their respective ruling planets), not all of the canon zodiac signs are the best fit for the characters. Some characters would actually fit better in very different zodiac signs based on their personality traits and motivations.
Aries: Rei
Aries are often noted for their impulsivity. As Sailor Mars, Rei doesn't actually exemplify that particular Aries trait. Instead, she's a great example of their passion. Nothing is more important to Rei than her place amongst the Sailor Senshi and helping them save the world.
She also has that Aries confidence. Rei is always secure in her convictions, even if the rest of the team might not agree with what she says. That trait is taken to the extreme in the '90s anime, making her butt heads with Usagi on a regular basis.
Taurus: Michiru
Canonically, Michiru is a Pisces, one of the lesser-known facts about her character. And the water sign lines up with her planet as Sailor Neptune. But she's not quite the dreamer that a Pisces is and the Taurus sign is a better fit for her.
Taureans tend to appreciate the finer things in life. For Michiru, that's her partner's sports cars and the classical music she plays on her violin. They are typically creatures of habit, focused on keeping their routine intact and the people around them safe. Michiru uses her visions to attempt to keep everyone safe, from her teammates to the entire rest of the world.
Gemini: Chibiusa
Chibiusa enters the franchise from the future, shaking things up, as it's initially not clear if she's an enemy or an ally. She proves herself trustworthy, but even as a young child, she also proves herself capable of adapting to the strangest of situations.
This adaptability is a sure sign of a Gemini. Geminis are usually social creatures, quickly able to charm new friends. While Chibiusa might be a little hostile when it comes to Usagi, she does turn on the charm with everyone else. She also manages to survive in a hostile environment and a whole different world.
Cancer: Usagi
With a birthday on June 30, Usagi is a Cancer within the universe. In canon, Sailor Moon actually shares her birthday with her future daughter.
Cancers have a reputation for being incredibly emotional. Usagi certainly demonstrates that throughout the series as she showcases her own feelings - even in the middle of a confrontation with villains. Her willingness to embrace her emotions, however, also makes her incredibly empathetic and willing to try to befriend and forgive the villains she battles.
Leo: Mamoru
While the Sailor Senshi each draw power from a different planet in the solar system, Mamoru is the protector of Earth. He's just as connected to the planet as he is to Sailor Moon herself.
Leos are usually known for their tendency to be the center of attention. While Mamoru isn't necessarily someone who tries to get all the attention, he is a natural charmer. He also has that Leo loyalty. Once he meets the Sailor Senshi as Tuxedo Mask, there's nothing he won't do to help them achieve their goals.
Virgo: Ami
Ami, as Sailor Mercury, is the brains behind the Sailor Senshi. It's not that the rest of her teammates aren't smart, it's just that she's more likely to analyze and plan things for everyone else.
This analytical mind and tendency to form a plan is straight out of the Virgo playbook. Virgos are the list-makers and mom friends. That's why Ami is the one put in charge of planning study sessions for the group when they're not busy saving the world.
Libra: Minako
Though Sailor Moon might seem like the leader of the Sailor Senshi, she's really the princess in fighting mode. The true leader of the team is Sailor Venus. Minako struggles to balance the life she wants with her sense of duty to the Sailor Senshi, and this attempt at balance is just part of what makes her a Libra.
Her charm rivals that of a Gemini, but as a natural leader, she's a better fit for Libra. Libras tend to be natural diplomats, diffusing tension and seeing all angles of a situation. Minako is this for her team, maintaining as much order as she can, even while she dreams of finding the perfect boyfriend or becoming a singer.
Scorpio: Haruka
Scorpios are often type-cast in fictional properties as villains, but that's an unfortunate misconception about the sign. The misconception comes from Scorpios aggressively going after their goals and desires. For Haruka, this aggressive attitude is focused on saving the world.
Of course, Sailor Uranus also embodies the Scorpio trait of secrecy. Scorpios tend to keep to themselves, not wanting to open up to others until they trust them completely. When Haruka, Michiru, and Setsuna first meet up with the other Sailor Senshi, it's Haruka who leads them in keeping themselves separate and secret, trying to feel the situation out.
Sagittarius: Artemis
While Luna tends to get most of the attention when it comes to the advisors for the Sailor Senshi, Artemis deserves some love too. He links up with Minako as she discovers her Sailor Senshi identity and helps her travel across Europe fighting evil in the Sailor V series.
Artemis is more of an optimist to Luna's natural state of worrying about the girls. He tends to trust Sailor Venus to do the job. He also, however, has that Sagittarius trait of being incredibly blunt, often not thinking before he speaks. Like Luna, he freely dispenses advice and tells stories, another trait of the Sagittarius philosopher.
Capricorn: Setsuna
Setsuna is one of the most mysterious of Sailor Senshi. Sailor Pluto is initially far removed from the others, duty-bound to guard the door that allows travel through space and time. Her staunch focus on her duty is just one of the things that make her a Capricorn.
Capricorns are all about hard work and keeping their responsibilities in line. They also focus on their family. While Setsuna doesn't appear to have a family of her own, the Moon Kingdom's royal family might as well be hers. The only thing that could get her to break her sacred duty is helping Chibiusa and her parents.
Aquarius: Hotaru
Despite being younger than the rest of the young women who become Sailor Senshi, Hotaru stands above the rest in her rise to become Sailor Saturn. Sailor Saturn and Hotaru, unlike the rest of the Senshi, are two distinctly different personalities. Hotaru, however, embraces the Sailor Senshi inside her, knowing how important it is to help her friends.
Hotaru is someone who forges her own path in the world of the Senshi, just as an Aquarius would. Aquarians are often seen as the most humanitarian sign of the zodiac, the ones interested in philanthropy and throwing their weight behind a cause. Hotaru does exactly this when she allows Sailor Saturn to call the shots.
Pisces: Makoto
In canon, Makoto is actually a Sagittarius, but the sign of the philosopher isn't the best fit for her. Instead, the fish is better, despite her not having power associated with water.
This is because Pisces is the sign of the dreamer. Pisces tend to get lost in their daydreams and they imagine their perfect world just as much as they live in the real one. Sailor Jupiter has to take care of herself, which means she's plenty grounded in reality. It also means that she has a lot of dreams she has no trouble vocalizing. She's a bit of a romantic and the perfect fit for a Pisces.