Friend of the jolly devil (1987)

A woodsman find and abandoned child in the forest and raises him as his son. When the child reaches 10, the woodsman suddenly goes blind. The kid is determined to help his "father" and answers a mysterious call. He must seek the Spirit of Darkness and defeat him if the woodsman is to see again. During his search for the Spirit he encounters a friendly monster who helps the boy in his quest. They are able to survive every dangerous test on their way and the final confrontation.