Villain! I Once Protected the World, Now I’m a Demon

“I've guarded the Sea of Tombs for ten thousand years. I only had to make it through tonight, and my mission would have been complete!” “But now everything has gone to waste. Tens of billions of demons have broken out of the tombs!” “This is all because of you idiots who call yourselves the Sixteen Great Clans!” “The Sixteen Great Clans? Hahaha, the Sixteen Great Clans...” “You were nothing but brats whom my revered master saved on a whim...” “I was the one who taught you everything you know!” “How did the merit of spending ten thousand years refining demons to protect the world become yours?” “Your sixteen ancestors received my divine weapons and inheritance, then knelt before me and swore to build a fortified city around the hundred-thousand-mile Sea of Tombs!” “They swore that their descendants, generation after generation, would guard the Sea of Tombs!” “But not only did you break your promise, you stole the credit for my and my master's deeds and deceived the world!” “Now your descendants have even released tens of billions of demons just to seize my treasures!” “They even reduced my master's bones to dust!” “Every one of you from the Sixteen Great Clans deserves to die!” “Even if every last one of you from the Sixteen Great Clans paid with your lives, it still wouldn't be enough!” “Since you've betrayed your oaths, don't blame me for showing no mercy!”