Doomsday: I Have A Farm Town

"A HK-UMP 45 submachine gun blueprint, because the key parts have been omitted, the gun's lethality after production is almost zero."
Looking at the submachine gun blueprint in front of him, a young man helplessly opened his eye cover.
Why is she so eager to build a gun? 
Because after 24 hours, the apocalypse is coming!
[Ding! Doomsday Survival Game has officially started! Player match ready!]
[Doomsday Survival Game is about to be activated. Disaster is coming. Host, please prepare!]
[Mission Distribution: Upgrade Home Defense System!]
Could he be ready for what is about to come?
...
After a few mouths later
A sudden disaster had swept the world, It had killed and mutated large areas of plants and animals. 
Food was scarce, monsters were rampant, nature order is chaotic...
The few at the top control the distribution of food, the bottom of the human become slaves and machines...
Every body knows, The human race was driven to near extinction. 
Now in this world only the laws of darkness exists.
Except for one place...