I've never had my Sun in anyone's 6th house, but I've observed my mother, who has her Sun in my father's 6th. And countless composites charts of relationships with 6th dynamics. I also don't know the nature of your relationship with said person. But from all this I can say:
1. There is an active servile dynamic going on. One will be servile to the other.
However, a relationship always needs to be taken and evaluated as a whole, not parts. My mother may be servile to my father, with Sun in his 6th, but in other parts and synastry of the relationship, my father contributes to what my mother needs and desires.
So as a whole, because both parties are getting something out of it, I don't discount a 6th placement as "unequal" in the traditional, generalization sense. Perhaps there is a definite hierarchical difference outwardly.
2. The second observation I can make would be area of impact. This stays true both for synastry and composite. My mother impacts my father the most (in his life) in daily running of the household, a supportive dynamic as a helper, and taking care of odds and ends of 6th house matters that makes daily life go smoothly. I believe he may even value her due to this, and she feels she's needed and necessary.
I would conclude if the relationship does go forward, your Sun, Mercury, Pluto are likely to have a power punched impact in the native's 6th domain. For you, you may feel like you want to help or assist this person.
As far as synastry feelings goes, personally I feel planetary interactions so much more, but not necessarily house interactions.
I'd venture to say whatever chemical interplay that's going on above, are the results of the planetary contacts (are they making conjunctions? Is your Pluto on his sensitive moon making him uber uncomfortable? What are the other aspects to his moon?). Thus much less to do with the house.
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