The fourth house can be a very important and critical position for Pluto in a composite chart. The actual effects of this can vary considerably. For instance, the fourth house rules the past. Therefore you may find that past circumstances have a stronger than usual conditioning effect on the course of your relationship.
The fourth house rules the deepest levels of the unconscious mind, so the two of you may act out very deep, unconsciously motivated patterns that change the course of your relationship.
In a love relationship or marriage, one or more of your parents may have an unusual degree of influence on the relationship.
The fourth house also rules the home, and in a relationship that has a clearly recognizable home, very powerful forces may be experienced there. The problem is that home should be a place where you can get away from pressure, but with Pluto in the fourth house, home could be the place where pressure is most intense.
Whatever the effect of the fourth-house Pluto, it does provide for resolution of its problems, because it gives you the desire and the ability to get at the