Teacher Iko has a problem with pirates: They keep raiding his village, taking whatever they want. Dusty documents in the archives suggest a last-chance solution: summon a dragon to destroy them. Of course everyone knows dragons don't exist, so Iko is as surprised as anyone else when the summoning works.
The dragon refuses to help - his race were once slaves to humans, and he has no desire to become one himself. But in answering the summons, he created a magical bond between himself and Iko, which will have consequences neither of them can foresee.