Japan is a nation spread out over fourteen thousand islands, so it is no surprise that its relationship with the sea is embedded deeply within its legends and folklore. According to mythology, the islands of Japan emerged from the depths of the primordial sea when the first gods stirred the waters with a spear. This illustrates the importance of the ocean to the development of Japan as both a country and a culture. It is a force that birthed and has sculpted its landscape, influenced its history, and inspired its imagination.

Yōkai — spirits and monsters found in Japanese folklore — reflect the complex relationship between Japan and the sea over its long history. The sea has served as a conduit for cultural exchange with continental Asia while also isolating Japan and allowing it to foster a distinct national identity. It has acted as both a protective barrier, shielding Japan from foreign invasion, and a destructive force, unleashing devastating tsunamis upon its shores. It is a vital source of sustenance, providing fish and seaweed that sustain the nation’s diet, yet it is also a realm of mystery and danger. These aspects are reflected in the number and diversity of aquatic yōkai. Some are playful, others are deadly; some grant wishes, others destroy; some bring terrible curses, and others provide divine protection.

This manual contains over 100 illustrated entries divided over five chapters that cover a wide variety of Japanese spirits, with a heavy focus on aquatic yōkai and maritime myths. Each creature is described in detail, including its habitat, diet, origin, and legends based on translations from centuries-old Japanese texts.