Setsuna Meiō (冥王せつな?) is Sailor Pluto, she`s gurdian of time.
Pluto's first appearance is during Sailor Moon R, where she watches over Chibi-Usa in the past. She has a very special relationship with Chibi-Usa. She is the keeper of the Garnet Orb.
Setsuna is the oldest of the nine Sailor Senshi; in the R season, she is a college student while the others are still in middle of high school. Despite being the eldest, Sailor Pluto never assumes any type of official leadership role. Even among the Outer Senshi, she frequently defers to Uranus and Neptune.