Sōichirō Kuwabara is a young adult male characterized by grey hair, red eyes, and shoulder-length brown hair. He practices as a medical doctor, distinguished as an elite graduate whose top-tier medical school status makes him highly sought after by hospitals, granting him freedom to select his workplace.

During his medical training, Kuwabara met nurse Ren Nanase and fell deeply in love. Ren rejected his advances, claiming she was undeserving of him, though her precise reasons remained unclear to him. Her rejection and subsequent disappearance deeply impacted him. After earning his doctorate, he spent four years moving between hospitals in a relentless but futile search for her, hindered by the closure of her former workplace which left no trace of its staff.

Kuwabara eventually rediscovered Ren Nanase, but their reunion delivered a severe psychological shock. He found explicit photographs revealing Ren engaged in sexual activities with multiple men and participating in sadomasochistic acts. These acts occurred under the influence of Dr. Hirasaka, who had transformed her into a submissive partner. This discovery shattered Kuwabara's idealized image of Ren.

This trauma triggered a significant psychological shift. Kuwabara rationalized that reclaiming Ren required surpassing Dr. Hirasaka's level of perversion and sadism, unleashing his own latent sadistic tendencies. His behavior escalated into sexual violence, exemplified by his brutal treatment of Mana Kazama, a nurse infatuated with him who had offered emotional support. He subjected her to increasingly extreme and degrading acts, channeling his obsession with Ren into these violent encounters.

Kuwabara's actions reflect a fractured psyche, using sexual domination as a misguided strategy to cope with his fixation on Ren and position himself as a suitable counterpart to her corrupted state. His storyline ends with him still trapped in this cycle of obsession and violence.