“Water manipulation”—the supernatural ability developed by mankind in the 22nd century that made it possible to traverse the ocean depths. Minato Yamajo returned to his old academy as an instructor to teach aspiring water manipulator trainees and ended up with two under his instruction—Natsuka Hoshino, his bumbling, yet cheerful childhood friend, and Chloe Knightley, a celebrated genius with a disagreeable personality. Watching these two as they worked their hardest, Minato started to truly enjoy his time as an instructor. However, the arrival of an SOS from the depths of a submerged city signaled the end of those peaceful days. Enter a truly frightening story at the crossroads of depths and despair. None of us knows how this will end.