Maou-sama no Machizukuri! ~Saikyou no Danjon wa Kindai Toshi~ - Volume 1 Chapter 4

Seven years ago, after their breakup, he disappeared without a trace.

The figure of the Armada seems to be still riding the wind and waves in the Atlantic Ocean, and the gold of South America still seems to flow in continuously. As Alfonso from the Bourbon family returns to the Royal Palace of Madrid where he was born, the story begins here…

- Description from novelbuddy

Perhaps it is the choice of fate. As a senior otaku, Qian Lingfeng got the “steel shell system”. However, when he swept the world with the system, became a local rich man, made all kinds of beautiful women, opened a harem, and realized the ultimate fantasy of thousands of otaku, he found that things seemed far from simple!
When the end comes, biochemical zombies suddenly come down, fierce beasts are in power, bloodthirsty zerg roam to kill the world, and human lives are comparable to dirt. Where will weak human beings go in this world? Is humanity going to be extinct? Or … can an otaku save the fate of the human race?

- Description from Novelupdates