Michiru's talent, skills, and desires can all be described by her basic statistics: her name, her birthdate, even her likes/dislikes. Takeuchi Naoko, creator of BSSM, does a wonderful job tying all of Michiru's subtle details into her character and the "Neptune persona." Why else would Michiru collect cosmetics and hate mushrooms?
Michiru's full name is 海王みちる. There is some confusion over the romanization of this name, however, how you do it is probably correct. (Kaioh, Kaiou, etc.).[1] The english equivalent to michiru can be "to rise," 
"to be full," "to mature," or "to expire." "Kaioh" translates as "sea king" or "ruler of the oceans." The most popular translation is "Rising Sea King" although "Full Sea King" and "Mature Sea King" are also correct.[2] Michiru name probably best symbolizes her strengths as a senshi. She is both very mature in her duties and seems to be content or "full" with/of her life. I think some would gladly say that see's also "full of herself" due to her coldness and apparent vanity. The "Sea king" obviously corresponds to her power over the waves and the sea. Michelle Kaio is her English name which is unusually resonable considering the NA dub's track record.[2]
Michiru's birthdate is list as March 6, 1977 which made her 17 when the S series anime premiered in Japan. A Pisces by nature (like me), she "possess a gentle and patient" character. Pisceans "accept the people around them" and "patiently wait for problems to sort themselves out."[3] Michiru's first encounter with Haruka in Episode 106 exemplifies her patience and gentility. Haruka constantly denies her destiny and acts very coldly towards Michiru. Michiru quietly takes her harsh comments and does not push Haruka towards any decision. Even when they happen to meet on the stairwell, she remains calm in front of Haruka's stubbornness and anger.
Pisceans are very artistic and may gain fame and money for their talents, though they do not seek physical wealth. Michiru is an acclaimed violinist and loves music class. Her violin is a very expensive Stradivarius so she must be loaded! However, Michiru appears play for love of it, on and off the battlefield. Her technique gained her entry into the Infinity Academy (Mugen Gauken) and infiltrate its student body.[4]
One of Michiru's most reliable Piscean qualities is her understanding and observation. She is very perceptive and intuitive; why do you think she knew of the approaching silence before Haruka? Her Deep Aqua Mirror also reflects (hee hee) her very keen mind. In Act 24, she notices Mamoru's noble eyes in her mirror and asks if he was a Prince in another life - how could she know that? The mirror "sees" the true "face" of the one who looks in it just like Michiru "sees" the truth inside the people she sees.
"O" is Michiru's blood type, and - according to Japanese mythology - a determining factor for her personality. O-typers "set the mood" and "create harmony" (get it?) in a group. They are usually seen "'taking it easy'" and looking "peaceful and carefree." Michiru's whole image is that of a very calm person.[5] 
Whenever Michiru enters she brings such a calm atmosphere that some can't help but admire her. Usagi, especially, admires Michiru for her maturity and "cool" nature. She follows her around trying to learn to be classy and professional in order to impress Mamoru.[6]
O-typers work better "by themselves or in subordinate positions." They would fear managing a task in its entirety, "worrying ... that [it] would fall into crisis."[5] This Piscean trait helps to justify Michiru strong desire for Haruka's company. Have you not wondered why she searched for a partner in Episode 106 and didn't try to save the world on her own? I believe Michiru was unsure of what she would do if she held the life of the world in her hands. Her mind is ready for such a feat, but she herself doubts her own skills too much. The earth is already falling into a crisis; does she want to help further it? When she saw Haruka, she was very much drawn to her confidence and strength. Perhaps she would be the one to make the right decisions for her ...
Michiru's favorite dish is Sashimi (刺身). A Japanese delicacy, sashimi consists of very fresh [and thinly sliced] seafoods "served with "dipping sauce, a simple garnish, and shredded daikon radish" (a very exquisitely prepared meal). It is traditionally considered to be "the finest dish in Japanese cuisine" and is recommended to be "eaten before other strong flavors" which may affect its taste.[7] Michiru really enjoys the "finer" things in life! She must like sashimi because of its refined reputation and elegant design. No great art can be rushed, she values the time and preparation it takes to create such a delicate dish. When it comes to food, Michiru will sacrifice time for taste.
Which brings me to Michiru's least favorite food, kikurage. Kikurage (キクラゲ) is a sort of mushroom that has a "dark color, [is] crunchy, and [is] flavorless."[8] Mushrooms are commonly associated with decay and unsanitary conditions even though they taste pretty good when cooked. Michiru must be turned-off by its tastelessness and bland look. Who would dare serve such a "lowly" scrap to the "king of the seas" as food?!
Michiru is most closely associated with the colors of aquamarine and teal/green. Aquamarine is given the symbols of "hope, youth, health, and fidelity." In mythology, Aquamarine (the gemstone) is "Neptune's gift to the mermaids" and "protects 
mariners as they sail the vast oceans."[9] Obviously, it's lore and history ties right in with Neptune's power over the sea.
Probably the most "conceited" hobby of Michiru's is her interest in collecting cosmetics. This does support many Neptune-haters' idea that Michiru is "uppity" and "vain." Michiru values beauty and everything elegant. She most likely collects cosmetics because they enhance one's own beauty and have the power even to create some aesthetic from something replusing. It's not her way of saying "look I'm so beautiful" but rather "I enjoy all things beauty-related." Michiru's cosmetics' fetish is also supported by her constant contact with her mirror; she's almost always checking looking into it!
Michiru appears to dislike sea cucumbers, worm-like echinoderms on the sea floor. They are generally scavengers and mostly each organic sea material. Sea cucumbers have a surprising defense mechanism: the can "expel ... their internal organs when startled by a potential predator." (Don't worry, they regenerate organs.) In Japanese haiku poems, they are called "sea slugs" because of their "neat little brain." One scientist calls these "slugs" the opposite of humans: "we [humans] have brains and are made of dumb material, while they [sea cucumbers], lacking brains, boast smart material."[10] Yea, I'm disgusted too.
1 Romanization: Ten'ô, Kaiô, and Meiô. Dies Gaudii.
2 Neptune: Kaioh Michiru. Sea Sky, Wind Water.
3 Aquarians. Astrology-online.com.
4 Act 24. Infinity Arc. Sailormoon Manga.
5 Blood Types. Castle in the Sky.
6 Episode 93. Sailormoon Super Season. Anime.
7 Sashimi. Wikipedia.org.
8 Kikurage. Japanese food glossary.
9 Devlin Jewelry Design. Wikipedia.org.
10 Sea cucumber. Wikipedia.org.