Doomsday Spiritual Seed

In the year 2100 in another world, scientists accidentally discovered a way to enter other cosmic planes. However, this discovery did not bring a better future to mankind. Instead, it attracted a large number of invasions from alien creatures. Humanity fell into a long dark age. Tens of billions of humans were slaughtered and only 1.3 Billion people remained. Can mankind hold on to this last homeland? This novel and its characters are purely fictitious. Any similarity is purely coincidental and should not be imitated.