I'm Building a Highland in the Wilderness

Traveling through a fantasy world, only to find that it has been occupied by demons and humans are barely surviving? Don't panic, here comes a soldier first. "You purchased melee minions x1000." "You purchased x1000 of remote minions." "You buy super soldiers x10" "If the cumulative consumption reaches 5,000 gold coins, the defense tower and life crystal will be opened." Come on, I'll lose if I can get to the high ground! This novel and its characters are purely fictitious. Any similarity is purely coincidental and should not be imitated.