Sun in 1st House Synastry is an aspect of spiritual teaching.
The partner’s will acts directly on you; in other words, this person tells you: “You have to be like this and like this,” and you have to obey, at least superficially. But this obedience is illusory if you yourself, from the inside, do not meet the changes that are happening to you at the will of your partner. Generally, you will perceive such a partner very personally and even painfully, if your 1st house is damaged; and the harmonious aspects of his Sun will exacerbate rather than palliate your reactions.
Your reactions, however, can be very misleading to your partner since, while it may seem that you obey their will, you will oppose it in the matters that are serious to you, although you won’t make it obvious. Therefore, it can be very difficult for your partner to resist your sincere impulses which quickly “turn him on”, literally forcing him or her to take initiative.
At a high level of paired relationships, Sun in 1st House Synastry is a very creative aspect for your partner because as little as a look from you can inspire them. If the relationship develops badly, the partner will seem to you as a cruel and inexorable tyrant whose main purpose is to humiliate your human dignity and destroy you as an independent person. You, in turn, appear to your partner as an impertinent and disobedient slave who has a peculiar power, but whom he must nevertheless train, break his pride and lead to an acceptable appearance (what exactly will show the synastric aspects of the Sun as a whole).
by A. Podvodny
Sun in 1st House Synastry Explanation
If the solar potential of the will and creation of one personality is aimed at stimulating the same qualities of another personality in 1st House then, speaking about their relationships, it can be argued that these individuals will be either in a state of competition, or in a state of cooperation when solving mutually interesting goals and tasks.
Since Aries is the natural ruler of the First House, in this situation both personalities will strive to improve each other until they become almost similar in their life views and positions. This state of affairs, taking into account the desire of everyone to play an equally important role, very obviously should lead to their close cooperation on the basis of competition. At the same time, both personalities without special infringement on pride are ready to hide their egoism away if their cooperation is obviously highly effective.
The romantic and intimate relationships of partners with Sun in 1st House Synastry are characterized by a strong mutual attraction. This is because the Sun is the natural ruler of the Fifth House, and the Ascendant affects the physical body of a person.