Natural Phenomenons of the sea
The threatening storms, loud thunders, ambiguous fogs, devouring whirlpools were phenomenons unexplainable to early human. As human's fear and imagination began to fill the gap of the nature's mystic, powerful and massive monsters became the raiser of such disasters.
These monsters had the ability to cause supernatural forces that seemed truely impossible and appear in various myths and folklores.
Bakunawa / Charybdis / Shen