Setsuna Meioh (冥王 せつな Meiō Setsuna) is a character in the anime Bishōjo Senshi Sailor Moon. As a Sailor Senshi, she is Sailor Pluto. She is known in the English dub as Trista Meioh.
She is the oldest of the Senshi, either around her twenties or much much older, depending on the adaptation. Her eternal duty is somewhat vaguely defined as "to guard the gates of time." Sailor Pluto was not introduced until late in the Sailor Moon R series.
Sailor Pluto's precise abilities and knowledge of the past and present are only vaguely defined, although it seems fandom incorrectly assumes a weak 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. (Note: This differs greatly from the manga, and may be a simple continuity error rather than bad writing.)
Sailor Pluto was the Senshi that Chibi-Usa contacted through Luna-P. Sailor Pluto was very fond of ChibiUsa, and referred to her by her "princess name," which is "Small Lady."
Sailor Pluto appears in just a few TV episodes, and observations show that she really has only one true attack, "Dead Scream"; unlike the other Senshi's attack phases, "Dead Scream" is whispered rather than shouted. (In the English dub it is known as "Pluto Deadly Scream", and it is yelled out like the others.) Sailor Pluto wields a weapon, a long key-shaped staff with a garnet jewel at its top, through which she focuses her power.
Another power Sailor Pluto possess is the ability to stop time, though it has been forbidden due to its potential for negative consequences. However, like the other rules set upon her position (never to leave the time gate and never use it to transport others), it was broken. While Sailor Neptune and Sailor Uranus are in the front compartment of a helicopter going to the "Mugen Gakuen" establishment, the demons that have surrounded the school attack the helicopter, immobilizing its rotors. As the helicopter was almost about to explode, Sailor Pluto used her time stopping magic to save the other passengers. While Neptune and Uranus were safely teleported onto the building, Pluto was thrown into a dimensional rift, and didn't re-emerge until much later (skipping an entire season in the anime version). It is uncertain if she wound up in the rift due to the nature of the power as a punishment for using it.
A small quirk occurs in continuity between the manga and anime. Pluto (temporarily) expires in both, but at different times; Pluto's death in the manga occurs much earlier and reawakens the good side of the possessed Chibi-Usa. However, for all intents and purposes, in the manga the technicality of Pluto existing outside time means she is able to be reincarnated as a normal woman while still existing back at her post at the Time Gate.
According to executive producer Janice Sonski, the final dub name chosen for Pluto, Trista, was chosen on account of the meaning of the name Setsuna. Setsuna can mean moment, but can also be a derivative of 'setsunai' meaning sadness. In the same vein, Trista, which derives from Latin's triste, also means sadness. The packaging of Irwin dolls released in Canada in 1998 called Setsuna "Celia".
In Japanese, she is voiced by Chiyoko Kawashima. In the English version, she is voiced by Sabrina Grdevich in Sailor Moon R and the movies and by Susan Aceron for Sailor Moon S.