Shin Hazama, a third-year high school student, is haunted by childhood tragedies—the deaths of his mother and later his father, whose demanding research at Izumi Heavy Industries left Shin emotionally isolated, burdened by unresolved grief. His guarded existence is persistently challenged by Kotori Izumi, a childhood friend determined to reconnect him with the world while balancing her family’s deep ties to the corporate entity linked to his pain.

Their fragile dynamic fractures when Shin meets Jin, a parallel counterpart from a feudal Japan where societal hierarchies dominate. Jin’s arrival exposes a lethal symmetry between their realities: deaths in one world trigger counterparts’ demise in the other, unraveling the mystery behind Shin’s mother’s death and subsequent losses. Driven by vengeance, Jin targets Kotori, whose alternate self, Princess Kotoko, enacts tyranny in his realm.

As assassins like Miko and Riko cross dimensions to eliminate threats, Shin’s protective instincts clash with Jin’s ruthless logic, forcing him to confront interdimensional warfare and the ethics of shared existence. His father’s abandoned research on parallel worlds surfaces, revealing Izumi Heavy Industries’ clandestine ties to the conflict. Torn between safeguarding Kotori and preventing cross-dimensional collapse, Shin battles external threats and internal scars, his resolve tested in a climactic struggle over identity, sacrifice, and the fragile threads binding disparate realities.