A Funayurei is a malevolent ghost that resides in the oceans and seeks to pursue and drown the living so as to add them into an ever-increasing spectral crew.
They often gather in large groups, sailing ghost ships, they will wander the waves with large buckets and try to sink boats by filling them with sea water, once a boat is sunk they will drown the sailors and add them to their ranks.
Sometimes Funayurei will grow into massive gestalt-forms in order to attack, in these forms they can be mistaken for Umi Bozu.
In order to escape Funayurei sailors would either toss food overboard to appease the hungry ghosts, charge into the ghost ship (running risk of disaster if they accidentally rammed into a real boat) or outsmarting the ghosts by giving them buckets with holes in the bottom, meaning no matter how hard the ghosts tried to flood the ship they'd be doomed to failure.