Setsuna Meiou was the civilian identity of Sailor Pluto, and appeared in the Sailor Moon anime, manga, musicals, and video games.
As Sailor Pluto, she guarded the Space-Time Door, and she originally could not leave her post, which left her very lonely. However, Neo-Queen Serenity allowed her to leave her post to help the other Senshi of the Outer Solar System during the events of the Sailor Moon S season, and she was reincarnated as an adult in the present time during the Death Busters arc, where she took on the identity of Setsuna Meiou, a K.O. University student studying physics.
Setsuna dreamed of being a designer one day. She was good friends with Chibiusa and Diana, and was also very close to Hotaru Tomoe after the end of the Death Busters crisis. In the manga, she lived in a house with Haruka Tenou, Michiru Kaiou, and Hotaru in the Dead Moon arc and Stars arc.
In the musicals, Setsuna was much less serious and more playful, even referring to herself the Madonna of the school infirmary. She would make jokes with the Three Lights and Usagi, who in turn teased her relentlessly about her age; when Setsuna asked to join Usagi's amateur detective group, she was labelled as an old woman in disguise. Despite her teasing of the younger girls, she always encouraged them to do their homework and be strong Sailor Senshi. In Tanjou! Ankoku no Princess Black Lady and its revision, she was revealed to live a very lonely life guarding the Space-Time Door, and valued Chibiusa's friendship. She also sympathized with Queen Beryl's love for Prince Endymion, comparing it to her own love for King Endymion, and helped the Queen to escape from Sailor Galaxia's wrath. At one point Usagi compared Setsuna to her mother.
Chibiusa's incantation to activate her Key of Space-Time referred to a "time guardian" and "the father of the guardian, Chronos," which has led some fans to speculate that Sailor Pluto was the time guardian and the daughter of Chronos. In the manga, Sailor Pluto also made several references to being the daughter of Chronos, and in Act 19, King Endymion told Sailor Venus that Pluto "carries the blood of the god in charge of time, Cronos [sic]." Setsuna became part of an adoptive family with Haruka, Michiru, and Hotaru when they took up residence together.
- In fan canon, Sailor Pluto and King Endymion are a popular couple due to some fans' interpretations of comments made by Sailor Pluto about Endymion in the manga. The idea of Pluto being in love with Endymion was mentioned in some of the musicals, especially in the song "Onna no Ronsou."
- Setsuna being Mamoru in drag is a long running meme/online gag that came from the alt.fan.sailor-moon newsgroup.
- Setsuna has a mortal fear of cockroaches.
- Her civilian first name has the same Japanese pronunciation as the Buddhist term meaning "split second."
- At the beginning of "Kaguya-hime no Koibito," Setsuna was shown purchasing alcohol. As one must be at least 20 years old to purchase alcohol in Japan, this could be a sign that she was at or older than that age at that point in the manga timeline.
- Setsuna was the only Solar System Senshi in the anime to invent a civilian identity for herself rather than have one before becoming a Senshi.
- Setsuna was the only one of the Solar System Senshi whose hair color in the musicals was not the same as it was in the anime.
- The word "setsuna" can sound like "setsunai" (切ない), which means "painful" in Japanese. Some fans have speculated that her name in the English dub, "Trista" (derived from the Latin "triste," meaning "sad"), was chosen to take advantage of this pun.
- In 1998, Irwin released a line of Senshi of the Outer Solar System dolls well before Sailor Moon S aired in North America. On the boxes of the Sailor Pluto dolls, she was given the civilian name "Celia."