When you start the game, you will play from the first episode, Mia. When you click on a character, a brief story summary cartoon appears, and when you start the game, all you have to do is survive for 10 minutes. When you defeat approaching monsters, you gain experience points, and when you level up, you can strengthen weapons, add skills, enhance passive skills, and recover stamina.
You can unlock characters by completing challenges during play. Each character has different monsters, map concepts, stories, weapons, speed, etc., so you can experience different pleasures.