As the two remaining ninjas in the world, Ijuin Rei and Ijuin Takeshi are twin brothers. Their family has a forbidden area that no one is allowed to enter. However, the two brothers went in because of curiosity, and then they met the destined person - Xing Min. The girl named Xingmin told their family secrets, so the two brothers made a decision to go to another world, gain power, and inherit the family business, no matter which one it was.