I Will Build the Underworld at the End of the World

Zombies are rampant and the undead are endless. The civil engineer protagonist awakens [underworld construction system]. While others are building walls, he is erecting "gates of hell" and paving "roads to hell." When the enemy attacks, the millions of heroes behind him make the gods tremble. Later, he discovered that this apocalypse was originally an "unqualified underworld" established by a certain existence...