Mio, my Mio portrays Bosse, a young boy who has been adopted by two elderly people
who dislike children. They harass him, and tell him to stay out of their way. One day he
receives a golden apple from an adult friend, and that same adult asks him to mail a postcard
which he is also given; he mails the card, but only after he has thrown a glance at the
it. It is addressed to a king, and it says that his son will be coming home soon.
Shortly after, Bosse finds a bottle with a genie trapped inside. Upon freeing it, the genie
recognises the apple and takes Bosse to another world far, far away.
In this world he is told that his real name is Mio, and that he is son of the king and thus prince
of the land. He finds a new best friend, and is even given his own horse. However, he quickly
learns that not everything in this world is as wonderful as it seemed at first. In the lands
beyond that of the king lives an evil knight named Kato, whose hatred is so strong the land
around his castle is barren and singed. He has kidnapped several children from the nearby
villages, and he poses a constant threat to the people living there.
Mio is told that he has been destined to fight Kato, even though he is only a child. So he and
his friend set out on a perilous journey into the land of Kato, as the stories have foreseen for
thousands and thousands of years.
Central themes in the story focus on friendship granting strength to endure hardships, that it
is sometimes necessary to leave a safe situation and put oneself at risk for a greater cause,
and that evil often coincides with unhappiness.