your name is Subaru Ariake, You were playing with your little brother(taiga), in this magical world where if a door spawns it has a rarity, Copper, Silver, And Golden. A golden door spawns in front of you but your little brother pushes you and gets the door. The door'll have a challenge for you to touch/kill the boss inside it, and your little brother came out alive and ever since that day. Your little brother treats you like a trash, you were bullied and a rainbow door spawns in front of you