The placement of Sun in the 7th house is considered to be an important placement in Vedic astrology. For Sagittarius Ascendant or Lagna, this placement becomes even more significant because the Sun is placed in its friend sign. Let's understand what impact this placement has on Sagittarius Ascendant.
First and foremost, for Sagittarius Lagna, the Sun becomes the lord of the 9th house along with Jupiter. The 9th house is considered to be a highly auspicious house in Vedic astrology as it governs higher education, religious beliefs, dharma, fortune, luck, etc. When the powerful Sun sits in the 7th house for Sagittarius Ascendant people born under such an influence are likely to have an inclination towards spirituality and philosophical pursuits.
The placement of Sun in its friend sign reflects positive traits that manifest through time spent with life partner ("other")-- Sagittarians born under this placement tend to have great rapport with their spouses and family members. They tend to attend various social events like parties, gatherings and conferences where they enjoy meeting new people.
Additionally, since the Sun also becomes a natural karaka for the first Lord or Lagna and 10th House representing career or profession (karma). Thus these individuals become optimistic about their lives and careers working hard with determination coupled with hope helps them achieve their goals quicker than average individuals.
As far as relationships go, those influenced by this positioning of sun tend to have distinct ego-boundaries that arise during interactions which make them persistent but also thick-skinned when something goes against them. Their strong personalities often help them establish themselves successfully socially and professionally but can get too dominating at times which can dampen their relationships.
Moreover, from this position in 7th house sun aspects its own Lagna or ascendant. This means that there might be significant changes in individual's personality over time especially after one gets married or enters serious relationships as the planet of ego and pride(Sun) looks upon its reflection in Lagna. They might become more ambitious, confident, and focused on their work goals: accomplishing them with diligence.
To sum it up, for Sagittarius Ascendant individuals who have Sun placed in the 7th house can expect to lead prosperous lives with good intelligence and communication skills, and a clear idea of their life's mission. They will likely have an affinity towards higher knowledge learning spirituality divinity etc., coupled with a successful career under the Sun's natural impact on karma or profession if they are harmonious in interactions with others. It is essential for such individuals to learn balance between self-presentation and being assertive when interacting with others.