As monster began appearing, the king worries of what would happen to his lands. He knows that something has to be done before all of his followers gets eaten by these horrible freaks. Fortunately, a young man volunteered to rid the land of all the monster. The king hesitated at first because, he don't think that the young lad could handle it, but accepted the offer since there is no other choice. It would be better to gamble on this young lad than not to do anything at all. He promises the young lad to assist him in any way he can.
The idea here is to shoot the enemy immediately as you him. You can't let it get close to you because he would beat you to death. You would earn money on each monster kill. You could use the money to upgrade your weapon. As you kill monsters, you earn some experience points. When you level up, you earn skill points, which you can use to learn new skills. as you move from one level to another, power enemies would be battling you, so you need to upgrade as soon as you can. You can't make it, if you won't upgrade.