Kyousuke Kousaka is an ordinary high school student who has had a strained, distant relationship with his younger sister, Kirino, for years. His life takes an unexpected turn when he discovers that his seemingly perfect, athletic, and model-student sister is actually a closeted otaku with a deep obsession for 'little sister' themed adult visual novels and magical girl anime. As Kyousuke becomes the sole confidant for Kirino's secret hobby, he is drawn into her complex social circle and the challenges of balancing her double life. The series explores themes of sibling dynamics, the stigma surrounding otaku culture in Japan, and the evolving emotional bonds between the siblings and their friends as they navigate the pressures of adolescence and personal identity.