I was summoned as a Dragon?!

Summoned Heroes have defended the Sailos Kingdom for thousands of years, from its enemies which inhabit the continent of Ethorn. However, the last summoning eventually backfired, and resulted in the 15 summoned heroes betraying the Kingdom, and establishing a Republic, which then swallowed half of Sailos' territory. 50 Years Later, the new King of Sailos decides to rely on the power of the Hero Summoning once more. But this time he wants to summon a great Dragon under his command. Unknowingly, this Dragon bears the soul of a human youth from Earth, and he has no intention of being a pet. ((Future events are more-or-less hazy, so bear with me.))