Setsuna is probably one of the most myseterious of the Sailor Senshi. Much about her is unknown, as the true facts about her past are questioned. It is said she was set to gaurd the gates of time since the Silver Millenium, and as the other senshi were reborn after the assult from Beryl, she remained at the gates until time passed, and the others were brought back again in the future.
Setsuna usualy keeps to herself, being a quiet woman. She keeps her distance from the inner senshi, not talking to them much, as do the rest of the outer senshi. She does however have a strong friendship with Chibi Usa, which she calls "Small Lady". Here Chibi Usa gives Setsuna her nickname, "Puu."
Sailorpluto first arrives in the R series, as the woman's image inside the eyes of Luna-P. She helps Chibi-Usa through her quest to find the silver crystal to help her mother in the future, and provides advice. She finaly shows herself when Chibi Usa's life is threatned in her dreams, and thus she helps the senshi be able to save Small Lady.
Although not much is shown of Pluto's personality besides a mature, quiet woman who sticks mainly to the outer senshi, we see a lighter side of her, in one of my favourite episodes of Sailorstars. When she and Venus are paired to face Nehelenia's mirror parodies, a bridge they were running on collapses when they are in the middle, causing them to fall. Luckily, Venus-chan uses her love me chain, and holds the two of them up. Despite their grim situation, Venus makes a light comment, causing Puu to giggle. ^.^ Twas very kawaii.
As for love interests for this senshi, there isn't much to say. It was rumoured in the manga that she had a crush on King Endymoin, but kept it to herself so she wouldn't jepordize the future any.
Sailorpluto's main attack she uses throughout the series, would be "Dead Scream" unlike the other senshi, she says this softly instead of yelling it. She uses her time staff to gather power around it, then hurls a purple planet shaped ball at her enemy. Her forbidden power, to stop time, was only used once in the S series. The consequence of it was fatal though, and she was persumed "dead". However later in the series she returned. Being one of the outer senshi, she carries one of the three talismans, the Garnet Orb. This is placed at the top of her staff, shaped like a heart.
Sailorpluto will always be burdened to gaurd the gates of time, but has also managed to make many good and loyal friends with her fellow Sailor Senshi. But only Pluto herself really knows who she is, and thus, she remains to be that mysterious woman, for eternity.