Is there any novel similar to the one I read a long time ago that I forgot its name? What was the general content?

The background of the story was that something had hit Earth in the future, causing a strange place to appear on Earth. There were all kinds of monsters in that place. People could go in and kill them to obtain energy, fur, and other things to sell for money. The large corporations of human society entered one after another, so as long as one had money, one could buy anything there. In order to earn money to treat his mother's illness, the male protagonist came to this place. When he entered, he met the female protagonist who had just escaped from the family. A physical book The level in the book seemed to be 1-star Warrior (Mage, Warlock...). 2-Star Warrior (Mage, Warlock...) Three-Star Warrior (…)... Nine-star Warrior (Mage, Warlock...) You can buy many weapons in that world (tanks, cannons, off-road vehicles…) Before entering that world, one's physique would be tested. According to different physiques, cards of different colors would be distributed. The male protagonist's card seemed to be all-rounded, and the female protagonist's profession seemed to be a gunner. The female lead's family was very rich. She seemed to be the daughter of a big family in Los Angeles. Other than the places that had been smashed, the rest of the Earth was intact. The social system was still good.