According to the japanese folklore, yōfuku are crab-like creatures with two arms and a back resembling a shellfish, a belly resembling a pufferfish, and a beak. They are found along the rocky shores of northwestern Wakayama Prefecture, and are also said to come from northern Fukuoka Prefecture.

Yōfuku live along the rocky shores of the Seto Inland Sea. For a brief period at high tide, they sing among the pebbles with a beautiful voice.

Shellfish gatherers sometimes catch yōfuku and, thinking them to be marvelous creatures, place them in a basket with sand and pebbles from the beach and take them home as pets. When their seawater is periodically changed, yōfuku stick their beaks out of the sand for a while and twitter in a beautiful voice that sounds something like a bamboo flute, the double-reeded flute called a hichiriki, or the string instrument called a kokyū.

Yōfuku comes from the yōkai scroll Chikuzen bakemono emaki, which includes a painting and a brief description of the creature. According to Chikuzen bakemono emaki, a boatman named Yaheiji from Goishizaki in Kii Province had a daughter who kept a yōfuku as a pet. Whenever she idly sang, the yōfuku sang along in a wonderful voice. However, it died after twenty days.