In Astrology, Mars represents sex and aggression, while Neptune represents illusions, dreams, and fantasy. When your Mars aspects another person’s Neptune, or vice-versa, a romantic bond is indicated.
In the case of the conjunction, square, or opposition, fantasy and romance permeates your relationship. The Neptune person is likely to see the Mars person as a knight in shining armor or protector. Indeed, Neptune admires Mars’ decisiveness, assertiveness, and toughness. Even if the Mars person is none of these things, the Neptune person will idealize the Mars person as though they were courageous and brave.
This aspect also indicates a sexual connection. The two of you fulfill each other’s sexual fantasies, and may even become addicted to one another! The Neptune person longs to be dominated by the Mars person, and is not afraid to be vulnerable around the Mars person. The Mars person is pleased with this role, as he feels more powerful in the presence of the Neptune person. The Neptune person may even become envious of the Mars person’s power and sexual prowess.
Neptune is likely to be dependent on the Mars person, which may provoke Neptune to manipulate the Mars person out of fear of losing him. The Mars person’s strength and sexual attractiveness may make the Neptune person nervous, so she may display evasive or confusing behavior which may confuse or frustrate the Mars person. Or, the Neptune person may try to gain Mars’ sympathy by playing the victim. Neptune may even resort to deceit, or sexually “teasing” Mars to keep his attention. This can lead to much frustration on the part of the Mars person; Mars is direct and open, so Neptune’s evasiveness, deceit, and dishonesty could lead to conflict and frustration on the part of the Mars person.
In the case of the trine and sextile between one person’s Mars and another person’s Neptune, fascination with one another is strong. The Neptune person idealizes the Mars person’s strength and sexual charisma, while the Mars person feels powerful and confident in the presence of the Neptune person. Together, the two of you work to fulfill each other’s sexual fantasies. The Mars person helps make Neptune’s dreams a reality. All in all, this is a very sweet aspect.