Sailor Pluto is one of those confusing, mysterious characters that are common in anime. Very little was known about her
in the 2nd season, except that she was the guardian of the time lanes. In the third season, we get to see Sailor Pluto out
of her Sailor guise as Meiou Setsuna, but even then we don't know much about her. Had she travelled back in time to help out
the Sailors or was this Sailor Pluto's form in the 20th century? Unfortunately, the anime never answered these questions.
Setsuna is a very private person. She almost never talks about herself; whenever she is talking to any of the Sailors she
is usually discussing how to defeat the enemy. The Inner Sailors respect her in a similar way that they respect Haruka and
Michiru, but they don't really know her, and don't have much of a relationship with her. However, Chibi-Usa (Rini) is shown
to be a good friend of Setsuna, and Chibi-usa often calls her "Puu." In a similar way to Usagi, Chibi-usa doesn't care that
Setsuna is mysterious, and treats Setsuna the way she would treat anyone. So Chibi-Usa and Setsuna have a better relationship.
During the third season, Sailor Pluto appeared with the third talisman, to the surprise of Uranus and Neptune. They realized
that they didn't have to sacrifice anybody to extract the talismans. The talisman that Sailor Pluto had is the garnet orb,
which attaches to the end of her staff (which, you'll notice, was missing during the 2nd season). Sailor Pluto had to take
a sudden exit during the end of the third season, when she used her forbidden attack "Dark Dome Close" to save the lives of
Uranus and Neptune.
In the fourth season, Sailor Pluto disappeared totally. She didn't even get a special, like Uranus and Neptune, explaining
why she was gone. Then, in the first several seconds of the fifth season, she appears to pick up baby Hotaru, explaining that
she needs Hotaru's power (these events are explained in the first Stars summary). Eventually it was shown that Hotaru, Michiru, Haruka, and Setsuna were all sharing the same house (aww... a big happy family
^.^). I think Setsuna appeared in one episode by herself of Sailor Stars to help out the Inners with Chibi Chibi, and it looked like Usagi and Setsuna had a similar relationship that Chibi-usa and Setsuna had. But besides that, she ended
the series more as a supporting character than a main character.