Apocalypse: I Rise as a Zombie King by Devouring

[Post-apocalyptic wasteland + arrogant villain protagonist + dark tone + evolution panel + stockpiling supplies + battle for supremacy among Zombie Kings] If you knew the world would end in seven days, and that you were certain to mutate into a zombie, able to evolve endlessly by devouring flesh and blood, what would you do? Zhang Yang, the son of a wealthy family, obtains an evolution panel. After learning that the apocalypse is coming and that he is certain to mutate, he swears to become the strongest Zombie King of the wasteland! To zombies, flesh and blood mean power. The more they devour, the stronger and more terrifying they become, with no upper limit! So Zhang Yang liquidates his entire fortune and stockpiles tens of thousands of tons of fresh flesh and blood! Seven days later, the apocalypse arrives right on schedule. While everyone else is fleeing in panic and losing sleep from worry, Zhang Yang devours flesh and blood in the safe house he built, evolving quietly and growing stronger by the day. By the time shelters and base cities have been built and the survivors are dreaming of standing against mutated creatures and reclaiming the land, Zhang Yang has become a Calamity Zombie King, capable of leading a billion-strong zombie horde to sweep aside everything in its path and reign supreme over the world! "My name is Zhang Yang, and I'm very arrogant!"