Kaito Iiyama (24) was living a monotonous life working at a publishing company with terrible working conditions. One day, he tries to help a high school girl who is being groped, but is falsely accused. Although the misunderstanding is cleared up, he is unfairly fired from his company because of it. Fed up with city life, Kaito returns to his hometown in the countryside. His parents have already passed away, and only his grandmother remains, but she is nowhere to be found. While exploring the dusty storehouse of his grandmother's house, he finds a mysterious mirror. It is a gate to another world, and Kaito gains the power to travel between this world and his own. It turns out that his grandmother was actually a powerful witch, and using the weapons and items he finds in the house, he levels up incredibly, becoming able to defeat dragons in one hit...!?