That Day the Greenskins Came

A relaxing and cheerful post-apocalyptic novel, the protagonist and villain have online IQs. The male protagonist has a very interesting personality. He is a delicate little man who can raise a kobold as a pet and be a hottie in Doomsday. Portable store system, defeat monsters, explode materials, and make equipment. There are also little greenskins and other monsters who can speak "Mabrimaka", exchange stone monuments erected everywhere, and the shocking secret discovered by the protagonist after leaving the Pacific Ocean.