Dororo Episode 18: Birabira the Sea Beast
Episode 18 of 26 of Dororo, aired August 2, 1969, 26 minutes. Available with English subtitles and dub where released.
Episode summary
Dororo and Hyakkimaru come to a fishing village. Dororo pulls out a harpoon from a rock just for fun. The harpoon, however, has contained a skeleton ray-monster called Bira-Bira. Hyakkimaru dives into the sea following Bira-Bira, which has escaped from underground to the sea. After a duel, Hyakkimaru disappears. The villagers think he must be dead. So in order to calm Bira-Bira`s anger, they throw Dororo and a village girl into the sea as sacrifice. Source: tezukaosamu.net