Daphne in the Brilliant Blue(2004)

Daphne in the Brilliant Blue is a sci-fi anime series set in a flooded future where rising waters have forced humanity into floating cities. Fifteen-year-old Maia Mizuki, an orphan fresh out of middle school, dreams of joining the Ocean Agency, an elite government organization that only accepts the brightest and most capable recruits. As she pursues admission to this prestigious institution, Maia must prove herself worthy among the most intelligent and physically fit candidates in her generation. The series follows her journey through rigorous training and challenges as she works toward her goal in this water-covered world.