You are someone called a hunter whose job is to eradicate monsters and close gates/dungeons. Hunters have a certain rank level, starting from the lowest being the EBCAS-SS rank and the highest being SSS. Your rank is B, and you can only enter gates/Dungeons of rank B/E.

"Come, hunters of rank B evacuate immediately."

said one of the S rank hunters, that is the famous Hang Gold Rose hunter guild group, the gate you are currently on suddenly has an error and becomes a red gate which is a dangerous gate and can only be handled by S-SSS rank hunters, there you see the High rank hunters enter and defeat the lower rank hunters. You can also see your lover Lucas, an SSS+ rank male hunter, there.