Doomsday: You Were Told to Save the World, but You Turned the Palace into a Wall

[Zombies + ancient setting + fictional world + no overpowered protagonist] In the third year of Yuanhe under the Great Wei, a plague of the dead breaks out, plunging the realm into chaos. A peerless swordsman, whose sword chills fourteen provinces with frost, becomes a Corpse King because he doesn't know the rule: “One scratch means death.” A senior monk from the Vajra Temple tries to chant sutras and guide the zombie horde to the afterlife, only to be gnawed down to his bones. In this world, I, Li Gou, am merely a useless illegitimate son with no inner power. But I know they can hear sounds, smell blood, and, most importantly, must be shot in the head! While others train in peerless martial arts, I stockpile rice... stockpile lime and spears. While others swear to defend the city to the death, I dig tunnels, set up barricades, and make homemade Molotov cocktails. “Li Gou is a coward who never leaves his home!” Then one day, a million-strong zombie horde surrounds the city, and the city's warriors wail in despair. Only my “Coward's Fortress” stands firm, its spears like a forest and its oil raining down, carving a path through the bloodshed! A savior? No, I'm just afraid of dying, that's all.