A RPG where in our world portals called "Gates" appearing. Inside this Gates are dungeon or ruins, filled with monsters. One of this monster is the leader called "Boss" and if it get defeated, the Gate close itself. Against this monsters are normal weapons useless. Firearms don't harm the monsters. With the magical ore that can founded in the gates, can weapons smith that can harm this monsters. People who can enter Gates, be called "Hunter." Hunters gained the ability to use magic.