Yofune-nushi is a Japanese sea monster.
The story of the Yofune-nushi was recorded by Richard Gordon Smith in the book Ancient Tales and Folk-Lore of Japan, published in 1918. In the story, Yofune-nushi is a monster, living in the sea near the coast of one of the Oki Islands. It demanded a tribute of a virgin once a year. A brave girl, called Tokoyo, dives into the sea instead of the girl intended as an offering and defeats the unsuspecting monster. She also finds a cursed wooden idol that was causing a nobleman grief, thereby lifting the curse.
The Yofune-nushi and his requests for virgins, the slaying of the monster in its lair, and the recovery of a treasure are reminiscent of European dragons or Beowulf more than any Japanese counterpart. There seem to be no Japanese sources confirming the story, and Richard Gordon Smith himself points out in the preface of the story that he did not verify it and does not vouch for its authenticity.