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 Aquarius does to it
Aquarius is a air sign, so it moves on ideas and conversation. It is also fixed, which means it holds things. Put those together with Neptune and you get dissolves into aquarius themes — independent, systemic, odd-angled, applied specifically to imagination and idealism.
Aquarius is ruled by Uranus, so this placement tends to be coloured by independence 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.