Natsume Asahina is an employee at a game company whose daily life takes an unexpected turn on the day of his mother's wedding to Rintaro Hinata. It is on this day that he learns he has gained a new step-sister, Ema Hinata, a young woman with a passion for video games. As Natsume begins to interact with her, he quickly becomes aware that he is not the only one in the Asahina household drawn to her. Ema has moved into the Sunrise Residence complex owned by Miwa Asahina, bringing her into close quarters with all thirteen of her new step-brothers. Natsume watches as his brothers—each with their own distinct personalities and ambitions—begin to develop romantic feelings for Ema, creating a complex web of rivalry and unspoken tension. Natsume himself grapples with his own growing emotions, torn between his desire to confess and his awareness that his younger brother Subaru, who has worked diligently toward his dreams without giving up, may be a more suitable match for her. The story unfolds from Natsume's point of view, exploring his internal struggles, his interactions with Ema, and the quiet competition among the brothers as they each vie for her attention while Ema herself simply wishes to build a loving family.