In the sixth installment of the Seishun Buta Yarou series, titled SUPERSTRING (OF FATE) THEORY, Sakuta faces a daunting predicament. His girlfriend, Mai, confronts the unsettling revelation that he has been cohabitating with his first love, Shouko, during her absence. As the trio grapples with the complexities of their intertwined relationships, the enigma surrounding Shouko deepens when her younger self requires hospitalization. Amidst the turmoil, questions arise about the aspirations of the young Shouko and the unexpected return of Sakuta's past flame. With mysteries unfolding, Sakuta finds himself at the heart of it all, unraveling the intricate threads of fate that bind them together.