Sailor Neptune (Kaioh Michiru) is the other Sailor that controls the forces of water, like Sailor Mercury. An Outer Senshi at odds with the original Sailor Team in the beginning, Michiru becomes part of the whole team in Sailor Stars. In Sailor Moon S, it is discovered that she carries the mirror talisman, which she now uses for one of her attacks.
Michiru likes to play the violin (and she's great at it!), and she's a really good swimmer (see the episode in Sailormoon S where she races against Ami). She goes to Juuban High School along with Haruka, Usagi, and the usual gang (except Rei of course) in the manga (comic). In the anime, she goes to Mugen, with Hotaru and Haruka.
As far as the prettiest Sailor Senshi is concerned, in my humble opinion, it would have to be Michiru. Her look is just elegance (even when she laughs; it just sounds so cool).
She is Kaiou Michiru, Sailor Neptune. 
