Sailor Pluto is not introduced until late in the Sailor Moon R series. She is the soldier who guards the gates of time. She is first seen contacting Chibiusa through Luna-P. Sailor Pluto refers to Chibiusa as "Small Lady." Chibiusa usually calls Sailor Pluto by the nickname "Puu" (subtitled as "Plu" in the S season subs). She acts as Chibiusa's guardian.
After the events of the second story arc, she leaves the gates of time to temporarily live as a human being, joins the rest of the Outer Senshi, and becomes a university student studying physics. The exact nature of how she leaves her post differs between versions; in the manga, she is reincarnated in present day by Neo-Queen Serenity after sacrificing herself during the second arc, while in the anime Neo-Queen Serenity allows her to leave. Even in her civilian form, Setsuna is the oldest of the Sailor Team, around her late teens or older. Her personality has been described as cold, impersonal, and somewhat lonely, however she does consistently display warmth and affection for Chibiusa. When she reincarnates, she becomes a bit less cold, but is still not very emotional. She later cares for Hotaru along with Michiru and Haruka.
Unlike the other Senshi, it is questioned whether she is fully human - she has been described as "a goddess, eternally guarding the Portal of Space and Time".
Sailor Pluto's precise abilities and knowledge of the past and present are only vaguely defined, although a common theory is a form of omniscience, possibly due to her portrayal in the anime. For example, she was presumably aware of the two sailor soldiers carrying the mystical objects they were hunting for, but did not inform them and allowed various people to be attacked. (This differs greatly from the manga, and may be a simple continuity error.) This omniscience is represented as being able to watch through the gates of time, and such.
Sailor Pluto appears in just a few TV episodes. Unlike Sailor Neptune and Sailor Uranus, she is sympathetic toward the Guardian Senshi, and assists them on several occasions. During the second story arc, she allows them to travel through time even though this is not ordinarily allowed. In the third story arc, she often extends help or advice to Sailor Moon and her companions even when Sailors Uranus and Neptune want the two groups separate. Later, Setsuna joins the Guardian Senshi in investigating the true identity of ChibiChibi.
Sailor Pluto has additional, less cited influences and spheres of dominion in her manga incarnation, influences that are vaguely suggested in the anime, but never made explicit. Sailor Pluto is much darker in her initial form in the manga, identified as the "Guardian of the Underworld" with very dark skin and a black sailor uniform. She is also stated to be the daughter of Chronos, god of time. She is a ruthless soldier who follows rather exacting laws, executing any intruders who dare violate the underworld in search for the Gates of Time. She nearly kills Sailor Moon before realizing who she is, stating that "all who break the taboo must be eliminated". Luna also states to the others that no one is to even know that she (Sailor Pluto) exists, due to her dominion and nature, and that to her knowledge no one has ever seen her. Luna calls her a "lone warrior," noting the sadness in her eyes.
In the manga, Pluto's death scene vaguely implies a romantic interest in Endymion, though this is never explored again. In the Sailor Moon musicals, Sailor Pluto has an unrequited love for King Endymion. It is explicitly mentioned in Eien Denetsu and Shin - Densetsu Kourin, in the song Onna no Ronsou ("Woman's Conflicts"). In the manga, it can only be inferred from depictions of Pluto blushing while around King Endymion, her reaction when he runs to comfort her during her death and in artwork depicting Neo-Queen Serenity, Pluto, and King Endymion. Various situations in the musicals have shown Pluto's unrequited love; for example, Tuxedo Mask's actor, Yuuta Mochizuki being leaned on by the actress of Sailor Pluto, Rei Saitou, and commenting on his new year's resolution: to be by Pluto's side.
A small quirk occurs in continuity between the manga and anime. Sailor Pluto (temporarily) expires in both, but at different times; her death in the manga occurs much earlier and reawakens the good side of the possessed Chibiusa. However, for all intents and purposes, in the manga the technicality of Sailor Pluto existing outside of time means she is able to be reincarnated as a normal woman while still existing back at her post at the Time Gate.
Setsuna is not shown using any special powers while in civilian form. She must first transform into a Sailor Senshi by raising her hand or a special device into the air and shouting a special phrase, originally "Pluto Planet Power, Make-up!" In the manga she eventually gains her Pluto Crystal and this phrase changes to evoke Pluto Crystal Power. In the anime, although she does upgrade to Super Sailor Pluto, the Crystal is never mentioned and her transformation is not shown on screen. When it is used, her transformation sequence involves a sand-like circle that rises up and washes over her, leaving her in her uniform.
Sailor Pluto's powers over time and space are somewhat tied with the destructive power of Sailor Saturn for astrological and mythological reasons. The names of Sailor Pluto's attacks include frequent reference to the Underworld, which was the province of Pluto in Roman myth; this is evident in her first named power, Dead Scream, which is her primary attack throughout the anime series. Unlike any other attack in the series, its name is whispered rather than shouted when she uses it.
Although her attacks all have English names (like those of the other Sailor Senshi), each is also given kanji in the manga to denote the meaning to Japanese readers. For example, Dead Scream is given kanji which translate to "ruin" and "wheezing" , with the intended English pronunciation given in furigana. In the manga, Sailor Pluto demonstrates a few other named powers, including Chronos Typhoon and the defensive forcefield Garnet Ball.
Sailor Pluto has enough power over time to stop it entirely, and although she is forbidden to do so, she uses this power one time each in the anime and manga. In the manga and musicals Tanjou! Ankoku no Princess Black Lady and it's revison Tanjou! Ankoku no Princess Black Lady [Kaiteiban] -Wakusei Nemesis no Nazo, she uses it to stop Prince Demand from touching the Silver Crystals of the past and future together, which would destroy the universe in a time paradox. In the anime, she uses this power to allow Sailors Uranus and Neptune to escape from a helicopter explosion. In each case, she sacrifices her own life as a result, but is reincarnated later in the series. Time Stop also appears as an offensive move in various of the Sailor Moon video games, seemingly without any penalty.
In addition to these powers, when the Space-Time Door has been misused, Sailor Pluto is able to close off passage to other worlds. At the end of the manga's third story arc, Sailor Saturn asks her to seal off forever the gateway to the world Pharaoh 90 had come from. This is done with Dark Dome Close .
All of Sailor Pluto's attacks require the use of the Garnet Orb, which is one of the three Talismans carried by the Outer Senshi. The orb rests at the top of her staff, the Garnet Rod, which is shaped like a giant key as a symbol of her stewardship over the Door of Space-Time. In the manga, she also wears a chain of keys around her waist, one of which is stolen by Chibiusa in order to travel back in time at the beginning of the second story arc. The Pluto Crystal is perhaps her most important possession, as it is her Sailor Crystal and the source of all her power, which becomes especially important in the fifth story arc. It is given to her by Sailor Saturn.