Sailorpluto is definitely one of the most admirable and intriguing senshi in SM, but I've also noticed that our beloved Setsuna is actually quite underrated, and that Pluto fans don't seem to exactly be piling up in abundance. What is it that keeps the fans away from Pluto? And what aspects of her character are luring those us who actually like her?
She is rarely seen in the Anime. This fact actually seems to work in her favor on both sides of the fence. A lot of the people who watch the anime don't really develop much of an attatchment to Pluto, because she generally only makes an appearance during times of real trouble, since she's committed to guarding the Gates of Time and Space, which is more than a full-time job. For Dub fans, Pluto is actually only seen ONCE, since they've only dubbed through the end of Sailormoon R, so people don't get the same chance to grow an attatchment to her. However, because she's rarely seen, it seems to give her a certain aura of mystery, and that very thing seems to be one of the most appealing aspects to the fans.
She leaves a not-so-great first impression. As you Setsuna fans know, Pluto first appeared in Sailormoon R, in place of the Chibiusa's Luna-P. Before that first appearance, Pluto is only heard, talking to Chibiusa through the eye of the Luna-P, so essentially, all you see or hear of her in this part of the anime is her half-pandering to Chibiusa. While it does show her fondness for children to some extent, you don't really get a sense for her real personality, so some might find her irritating because of this first impression, because she's likely to come off as patronizing.
She's uniquely beautiful. Setsuna is definitely one of the prettiest senshi, and her dark green hair and haunting eyes make her a very unique beauty. This aspect will make her more appealing to those who prefer a more original look. However, it's probably not going to score her many extra points with fans of Makoto, Minako, and Usagi, since they have the least outlandish hair and eye colors of them all.
She's powerful! Let's face it: Power can be appealing. Power can be sexy. Why do you think that ugly and unscrupulous men of power wind up married to such lovely women? ^_- And the power aspect can certainly work for Pluto too, because she's got power up the yin-yang. She's the controller of Time! She throws powerful attacks around, is able to stop time, and is a formidable warrior and opponent. That's pretty heavy on the power scale, ne?
She's a character that makes you think. Admittedly, Setsuna is not the easiest person to understand, as she is shrouded in mystery. People who are more the thinking kind would likely find that exciting, but some of the less insightful people out there are probably turned off by it. They can't really see what makes Pluto tick, because she's not always voicing her feelings and opinions as the other senshi are more prone to doing. So, because they can't understand her and relate to her as readily as other characters, they automatically decide that she's a lesser character, and pass her by without really seeing her finer points.
This theory came from Zero+: "As the oldest of the scouts she has this aura of mature femininity; a "real" woman if you will. Even Neptune and Uranus don't quite project this image. I guess some guys go for the school girl image while others go for the mature woman image. As a fellow otaku, you can surely agree that we like something different from the norm; if the norm is being into anime then being into an obscure character becomes cool, right?"
Well, I don't have all day to sit around analyzing the human psyche, so if you have anything to contribute, feel free to send me some input. Your comments may be posted here for the world to see, along with a link and credit!