What Neptune does in a chart
Neptune is the part of the chart that answers one question:Where do I dissolve the boundaries? It describes imagination and idealism — not events, and not outcomes.
What Libra does to it
Libra is a air sign, so it moves on ideas and conversation. It is also cardinal, which means it starts things. Put those together with Neptune and you get dissolves into libra themes — balancing, relational, fair, applied specifically to imagination and idealism.
Libra is ruled by Venus, so this placement tends to be coloured by love style as well.
The useful version
Placements are not verdicts. This one describes a default setting, not a limit — the things listed above are what you do when you are not thinking about it, which is exactly why noticing them is worth something.