The Hundred-Defeat Hero

"You have already fallen. Which means, you are now free to go mad with pleasure." The peaceful Kingdom of Seira is invaded by otherworldly races, leaving the kingdom on the brink of destruction. The noble Holy Knight, Estin, seeks the 'Black Crystal'—a treasure of the Demon King containing vast magical power—to defeat the invaders. However, the Demon King he finally encounters informs him that the 'Black Crystal' was sealed within the Demon Emperor's Tower, 'Zebryl,' a thousand years ago. He advises Estin that if he travels back a millennium and reaches the top of the tower, he too can obtain immense power. To save his doomed kingdom, Estin enters a contract with the Demon King, becomes ...