SSS Class Mecha Inventor

Year 3025....
A meteor came descending from the skies and it came destroying the north pole. Making the continent shook. It was a disaster and the north pole melted. Making a rise to the water levels itself.
A month after, monsters came out of nowhere and went attacking the cities and armies were deployed.
Monsters came and appeared, almost destroyed humanity. Almost half of humanity was taken and liberated in just a year. All thought that it was the end but nope. 90% of human territory was taken and only 10% survived due to having walls and barriers.
The geeks and cultured people that read novels all thought that there will be hope. But nope, no system came, no global awakening, no magic nor powers.
So only one way..... technology! Then it all made possible by one man. It was Renji....