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 or 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.
Black Lady was the form Chibiusa took when she was turned to evil by Wiseman.
In the anime, Chibiusa travelled to the future with the Sailor Senshi and once there, heard King Endymion tell them that the Silver Crystal disappeared shortly before the Black Moon Clan attacked.
Thinking that it was her fault that the Crystal vanished, and thus her mother was hurt, she became upset and ran away, leaving the shield around the Crystal Palace. Wiseman found her there and began showing her illusions that made her think that everyone blamed her for what happened. He told her that he could convince...