In astrological tradition, the Neptune governs imagination, dreams, and the dissolving of boundaries, while Aquarius is a air sign read as independent, inventive, humanitarian, and unconventional.
So Neptune in Aquarius is often read as a placement where where intuition, art, and longing tend to gather takes on a independent, inventive quality. Tradition holds that someone with this placement tends to dreams and idealizes in a way that feels humanitarian — coloured by the air-sign temperament of Aquarius rather than by any single rule.
None of this is a prediction or a fixed trait. These are tendencies astrologers have long associated with Neptune in Aquarius, and how they actually show up depends on the rest of the chart — the houses, the aspects, and the other placements that this guide cannot see.
A general guide to astrological tradition — tendencies, not predictions. It describes the placement in the abstract and is not about any specific person.