After Killing My Girlfriend from the Start, I Evolved into the Corpse Emperor

【Apocalypse + zombie evolution + no saintly do-gooder + no System + ruthless】 What kind of spectacular world would it be if zombies were ranked by the color of their eyes? From lowest to highest, the zombie ranks are white, black, yellow, orange, blue, green, purple, red, and gold. These correspond respectively to the ability-user cultivation ranks F, E, D, C, B, A, S, SS, and SSS. So follow the protagonist through the gates of this new world, and witness the rise of the zombie race under their leadership.