Composite readings

Composite Sun and Mercury

A composite chart is built from the midpoints between two people's charts, so it is one chart for the pair rather than a chart for either person. These readings say what a placement in it stands for in a pair's shared chart.

Together

Composite Sun conjunct with Mercury
The pair's identity and its way of thinking and talking tend to merge, so its ideas often sound like a direct statement of who it is.
Composite Sun in an easy aspect with Mercury
Conversation tends to carry the pair's sense of purpose naturally, and it can put what it stands for into words with little struggle.
Composite Sun in a hard aspect with Mercury
What the pair stands for and how it talks things through do not quite line up, so its words can say something a little different from its aims, or more, or less.

None of this is a verdict. A single placement never describes a whole relationship, and astrology is a tradition of interpretation rather than a body of established fact.