Mari always admired her older brother Tsuyoshi, who excelled in both academics and sports. But recently, after hitting rock bottom and becoming a shut-in NEET, he locked himself in his room—until one day, Mari suddenly received a proposal from him: "Let's play King's Game!" It was Tsuyoshi's impromptu idea. Being the devoted sister she was, Mari agreed. When the game concluded, Tsuyoshi became the king and issued her a strict command: "For the next two days, I'll remain the king, and you must absolutely obey every single order I give you!!"