Magic Boy has the distinction of being the second Japanese animated feature in color. The first was The Tale of the White Serpent (1958), released in the US as Panda and the Magic Serpent in July 1961. Since MGM distributed the English-dubbed Magic Boy in June 1961 (according to IMDB), it was the first to be seen in the US. That version is now available on demand from Warner Archive.
Sasuke is a boy who lives in the forest with his older sister and his little animal friends. When the faun’s mother is killed by a sea monster who is actually an evil witch (as indicated by traditional long black hair and chalk-white skin), Sasuke climbs a mountain to learn magic from a hermit. This takes three years, during which neither he nor the baby animals ever get bigger. After the obligatory training sequences, there’s a big fight—lots of death but no blood—in which he’s aided by the local handsome prince who’d been so unhelpful in saving the village from destruction by the witch’s army.