Chapter 0

Prologue is the introductory chapter of the Seinen manga Eiyū Kyōshitsu.

Short Summary
An unnamed, old lady is seen lying in bed with her granddaughter, reading her the story of how a boy with righteous heart, managed to defeat the Demon Lord who was terrorizing over the people. However, when the child asks her where is the hero right now, she replies that no one knows. Blade then appears in front of Rosewood Academy, yelling that from today onwards, he's a commoner.

Full Summary
The chapter opens up with an old lady lying in bed with her granddaughter, holding a big book in her hands. She starts recounting the story by saying that a long time ago, there was a man called The Demon Lord who wielded a very mysterious and very terrifying power that enabled him to turn the impossible into possible and hence to rule over the people. Because his power was growing larger and larger,no matter how many people challenged him, they all failed to defeat him, further driving the people to despair.

But then a boy with righteous heart who wielded a power identical to the Demon Lord's appeared and was proclaimed "Hero" by the people who put their hopes and dreams into him. After passing through many deadly struggles and trials on the long journey he and his comrades started, the hero finally reached the Demon Lord and eventually defeated him, after fighting a lengthy battle that lasted many days, bringing peace to the world. Upon hearing the story, the child asks her grandmother where did the hero go after his battle, but the old lady tells her that no one knows.

Blade then appears in front of Rosewood Academy with a briefcase in his right hand and after taking a deep breath, he yells that from today onwards, he's a commoner.

Trivia

 * The fact that Blade appears right after the old lady says that the legendary hero's whereabouts are unknown may be a hint that his true identity is the story's "Hero".