Daphne in the Brilliant Blue (2004)

In the distant future, the earth is almost entirely covered by the ocean, with only small islands and floating cities on the surface. 15-year-old Maia Mizuki is turned down by the prestigious Ocean Agency, despite her exceptional skills and superior grades. After finally being evicted from her home, she joins the Nereids squad, a group of bounty hunters who seek fugitives from justice and other dangerous missions.