Dororo to Hyakkimaru - episode 18 - 02 Aug, 1969

Dororo and Hyakkimaru arrive at a fishing village where Dororo foolishly pulls an old harpoon out of some rocks. This releases a skeleton ray-monster called Bira-Bira that escapes into the sea. Dororo is challenged by a girl called Sayo who demands that he return the harpoon. Hyakkimaru dives into the sea following Bira-Bira, but he disappears. The villagers assume he is dead, so to calm Bira-Bira's anger, they send Dororo and the village girl into the sea as a sacrifice. When the demon attacks them, Hyakkimaru appears and destroys it, causing his teeth to be returned to him. (Source: Wikipedia)