Neptune in 12th House synastry relationships are based on an intuitive connection at the subconscious level. The partners show mutual interest in research related to psychology and the hidden possibilities of human consciousness, they willingly engage in religious, humanitarian, and charitable activities. A karmic connection often arises between Neptune in Twelfth House synastry partners. The spheres of joint vital activity of these individuals are usually related to spirituality and creativity (culture, music, mysticism, etc.).
With Neptune’s negativity, the partners connive at each other in obstructive manifestations of human nature, which clearly does not encourage any constructive activity. Deceipt and substance abuse are likely.
from F. Sakoyan, L. Ecker
Neptune in 12th House Synastry Explained
Twelfth House is Neptune’s dominion, and your mutual understanding with this partner in mystical and religious experiences can be wonderful: they usually don’t require words as meditations go on their own. However, their nature may suit neither your partner nor you.
At a low level of spiritual development, Neptune in Twelfth House synastry provides copious opportunities for unscrupulous behavior, mutual deception, chronic misunderstandings that have existed for years and got brushed under the rug, and most importantly, to all kinds of speculations and demagogy on the topic of duty and sacrifice. The partner will be inclined to expect voluntary sacrifices and unselfish service from you because it is very difficult for her to live (it may not be any easier for you, but this does not concern her; besides, she may sincerely believe that to be your own fault. However, your service will not suffice: a Neptune in 12 House synastry partner thinks that she deserves better treatment and that you are guilty of the misfortunes happening to her. You will probably disagree but it will be difficult to formulate and explain your feelings about the situation.
Neptune in Twelfth House synastry requires you to drop the habits of begging, self-pity, and accusations. Here, it’s almost impossible to sort things out with your partner since the emotions are extremely entangled and confusing. However, even a small success can grow into a source of grace and the eventual resolution of your most intimate problems.
from A. Podvodny