Kosuke and Rikimaru: Dragon of Konpei Island (1988)

The OVA shows two brothers who are protectors of the island of Konpei. Both grew up struggling and followed their routine by training and hunting to have something to eat. For some reason the Dragons who inhabited the island are gone, and there remains only one. The Dragons of this island carry in their forehead a very beautiful jewel that covets some bandits. Kosuke and Rikimaru will protect the island and the Dragon at any cost, for if the last Dragon dies or leaves, the islanders, including them, are in danger of life.