Mars in 5th House synastry. Under this aspect, relationships between people are based on a strong romantic and physical attraction to each other; you can even say that physical attraction is a prerequisite for any romance.
However, the personality of the Fifth House considers the “Martian” one too crude and demanding. The latter, in turn, does not hesitate to show impulsiveness, especially in those areas of life that are associated with maximum pleasure and enjoyment.
If the people are immature from the evolutionary standpoint, and if the Mars is afflicted, their relationship becomes dangerous and can harm both parties both morally and physically through quarrels, financial losses, physical injuries, etc.
from F. Sakoyan, L. Ecker
Mars in 5th House Synastry Explained
If the synastric Sun in the Fifth House symbolizes the role of the Movie Director in your life scenarios, then Mars in 5th House synastry represents the Main Hero in them. In a female horoscope it can be a Hero-Lover, but not necessary: generally speaking, the role of the Main Hero can be the Boss, Husband, Friend, Enemy, Advisor: in short, anyone with enough power to bear the energetic inception of the plot.
For example, the afflicted Mars of a partner may initiate a lot of your troubles, which it will subsequently dissolve. Consequently, at the beginning of the plot this Mars in 5th House synastry partner plays the role of the Disturber of your Equanimity, then the Accused Criminal, and finally the Mighty Redeemer-Savior. All these changes and the associated events can proceed very powerfully but almost entirely on his energy, while you (especially if your Fifth House is weak) internally can remain almost unaffected by all this.
In general, Mars in Fifth House synastry is characterized by the following kind of misunderstanding. With your behavior you seem to invite your partner to play, but you mean a very specific plot, often with limited personal participation. The partner turns on strongly, even aggressively, expecting the same from you (because, after all, you were the one who invited him to participate). But it may be impossible to get true involvement from you, hence the partner’s frustration which sometimes ends in conflicts ranging from a threat to a war with or without declaration (depending on the position of Mars in your partner’s natal chart).
Working out the aspect can be very important for both parties: you will get more energy for your work, and your partner will be inspired to do great things requiring the power that they clearly would not have found on their own.
from A. Podvodny