Pluto in the 6th house in the natal chart has a laser-like focus, and often, this focus is directed towards the self: How can I improve myself, better myself, purify and cleanse myself?
With this position of Pluto, there can be an obsessive and compulsive pull to be "perfect", constantly seeking to work on the self. There can be a tendency to be hypercritical of the self, as for every improvement made, the barre is set a tad higher - like a hamster on a wheel, there is no stopping unless you decide to get off the wheel.
The upside of this position of Pluto is of course: Modesty, being humble, perfectionism, hard work, ethics, strong analytical capacities, cleansing power. With this position we often find people involved in work that requires a tremendous patience and attention to details: Researchers, accountant, people involved in organizational work / classification work.
The downside of this position of Pluto is that, there can be a tendency to have an internalized sense of guilt and shame. There can be a subconscious belief of being "bad", which can fuel an overall sense of self-loathing. The problem with self-loathing is this - you cannot change what you cannot see and accept, and it's nearly impossible to accept what you have hatred for. Here we find the concept of compulsion and repulsion of Pluto - compulsively attracted to bettering the self, and at times, repulsed by the self. The challenge of this position of Pluto is to learn self-compassion, self-acceptance (=Piscean values, opposite of Virgo which intent is to discriminate), which leads to being able to fully fulfill this Pluto's desires: Self-improvement.
Connected with this pattern, Pluto in the 6th house can also signify that you make up obligations for yourself to justify not having any time for yourself, this is a typical 6th House pattern and a form of personal avoidance.
The 6th House is associated with Virgo, and Virgo can become so analytic that it loses the big picture. I will use here the image of Jeffrey Green, who talks about a centipede, trying to understand what’s wrong with one of the 1000 legs. You stop and try to fix that one broken leg, but you forget that the other 999 work perfectly fine. The key with this position of Pluto is to learn how to not sweat the small stuff - easier said than done depending on the rest of the chart, but"mental paralysis" surely is a possibility with this position of Pluto.
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"Pluto an evolutionary journey of the soul": By Jeff Green
"The book of Pluto": Steven Forrest