Villain! I Once Protected the World, but Now I Have Become a Demon

"I have guarded Tomb Sea for ten thousand years. As long as I survive tonight, I will be done!" "Now we have failed, and tens of billions of demon gods have broken out of the tomb!" "This is all caused by you idiots from the so-called sixteen great families!" "Sixteen great aristocratic families, hahaha, sixteen great aristocratic families..." "You are just little brats saved by Master and his old man..." "I taught you all your skills!" "How come this tremendous achievement of refining demons and protecting the world for ten thousand years is your credit?" "When your sixteen ancestors received my magic weapon and inheritance, you knelt before me and swore to build a siege around the sea of 100,000 miles of tombs!" "Life after life, my descendants will protect the sea of tombs!" "But not only did you fail to fulfill your promise, you took advantage of me and my mentor and deceived the world and stole your reputation!" "Now your descendants are trying to steal my magic weapon and let the tens of billions of demons go!" "He also beat my master's bones into ashes!" "It would be a shame for each of you sixteen great families to die!" "It's not enough for you, the sixteen great families, to pay me the lives of all your people!" "Since you have betrayed your trust, don't blame me for being ruthless!"