High school student Kenji Koiso is an honest and introverted math genius. One summer day, he was invited to work part-time in the hometown of the beautiful senior, Jinnai Natsuki. It turned out that the content of the part-time job was to pretend to be Natsuki's boyfriend. The ancestors of the Jinnai family were a samurai family that fought a desperate battle with the Tokugawa Army. Hundreds of years later, the tough and tenacious character is still deeply rooted in the soul of this family. After the initial restraint, Kenji gradually integrated into this lively big family. In the world at that time, a network virtual platform called "OZ" was popular all over the world, and 1.6 billion people were fascinated by it. It has a defense system that is known as the most secure in the world, but its login password was accidentally cracked by Kenji. A mysterious hacker invaded OZ, and the virtual network and real society suddenly fell into chaos. In a critical moment, the Jinnai family regained the responsibility and honor of the samurai family and launched a tense and fierce summer battle with the destroyer AI...