Rebirth Before the Doomsday: My Underground Fortress Can Be Upgraded

In 2031, I was looking for medical supplies in an abandoned shopping mall, but was eaten alive by the zombie lord "Red Crown". When I opened my eyes again, I returned to July 17, 2029. There are still 365 days until the red tide biological crisis sweeps the world. The younger sister who died in the infection area of ​​the hospital in her previous life is still alive, and the Qingyashan mine left by her father has not yet been sold. At the same time, something called the "Doomsday Fortress System" appeared in my mind. It can scan the ground, unlock blueprints, and upgrade fortresses, but it won't give me steel, food, and loyalty for free. This year, I will compete for resources with time, capital, rules, and all those who do not believe in the end of the world. First dig a safe house and then build an underground city. When the red rain fell and people in the city started biting each other, they realized that I was not building a warehouse. I am leaving the last door open to humanity.