Junji Sagawa serves as the primary antagonist of the series, acting as the leader of the mysterious cult known as the Genuine Love Society. His background reveals that he was not always consumed by his eventual obsession. Under pressure from a childhood friend and following the discovery of the Master Stone, Sagawa became increasingly fixated on the world of Stasis, transforming into the driven and ruthless man encountered in the main storyline. His personality is defined by a cold and calculating determination, with his obsession overriding any previous intentions he might have had.

Sagawa's primary motivation is to master the nature of Stasis for his own benefit. His ultimate goal extends beyond simple control; he desires to use the stone to observe the entire timeline of existence, from the beginning of the world to the very end, believing that by harnessing the power of specters within Stasis he can spectate all of time. This desire to witness the future and control time itself drives all of his actions throughout the story.

In the story, Sagawa leads the Genuine Love Society in their conflict against the Yukawa family, with his subordinate Shiomi often tasked with carrying out his orders, such as retrieving the mystical stone possessed by the protagonist Juri. His role as the central antagonist puts him in direct opposition to the Yukawa family as they fight to rescue their kidnapped relatives and escape the frozen world of Stasis. His key relationships include his loyal followers within the cult, particularly Shiomi as his right hand, as well as the childhood friend whose influence helped set him on his destructive path.

Sagawa undergoes significant development as the series progresses. As his obsession deepens, he undergoes a monstrous physical transformation, abandoning his human form to become a Handler creature within Stasis. In the final resolution, when he is defeated, the story takes a unique turn as Sagawa is reborn as an infant. This new being retains the physical appearance of Junji but is mentally a blank slate, a new person whose future identity will be shaped by the social influences and family that raise him, effectively representing the mental death of the former villain. Regarding notable abilities, as the leader of the Genuine Love Society, Sagawa can operate within the frozen time of Stasis. This ability is attributed to the specters, or spirits, within him and his followers, which allow them to move and interact in a world where time does not flow.