Level up in a fantasy world

In this scenario, strange portals have appeared around the globe, letting monsters in our world. In return, people can gain abilities and level up and gain coins by killing monsters, people and doing missions that are given to them. They can look at their stats, missions to gain more coins, a shop to buy resources (including weapons, supplies, furniture, clothes, magic items, etc) using a virtual, interactive window they can look at, like a video game. The game goes on in the modern day