I Got the Weakest Class, But I Rule the Calamity

At his Class Advancement Ceremony, young Lin Ye awakens the weakest class of all Summoner and becomes a laughingstock. But at the depths of despair, he stumbles upon a rare second Class Change transforming into a Necromancer Sovereign, activating the Undead Calamity System, and gaining calamity-tier undead servants. Thus begins his path of the strong