Even after some time has passed since the sports festival, the feeling of invincibility continues. My relationship with my boyfriend is going so smoothly that life feels perfect! But suddenly, a pitfall appears in these days of bliss. "I'm going to become a truant." "Huh!?" My younger sister, Amaki Haruna, who is more talented than me, has become a recluse!? Watching my sister who only plays games at home every day reminds me of my past self, and I desperately want to help her return to school, so I reach out to the Quintet members. With the help of Ajisai-san, Satsuki-san, and Mai in persuading her, I am tormented by my own powerlessness as I realize I have no words that can reach my sister's heart. "I'm supposed to be the big sister!" What can I do for the sister who helped me with my high school debut!? The bond between sisters is put to the test in this sixth installment of the girls' love comedy!