Ren Nanase is a 22-year-old nurse at St. Juliana Hospital, recognized by her ankle-length claret hair, typically secured in a ponytail, teal eyes, and a slim physique with measurements of 87-57-87 cm. She initially projects warmth and kindness, welcoming new staff member Ryuji Hirasaka. Secretly, she maintains a relationship with inpatient boxer Naoya Ohkawa, engaging in match-fixing to aid his career. Ryuji discovers this secret and uses it as blackmail to coerce her into sexual acts.

Ren endures systematic psychological and sexual abuse orchestrated by Ryuji and hospital director Narumi Jinguji, manipulated into becoming a "sex slave" for a proposed hospital department catering to patients' sexual interests. Despite the abuse, she develops Stockholm syndrome, forming an emotional attachment to Ryuji that deepens into genuine love. This leads her to assist in recruiting other nurses into the exploitative system.

Her traumatic arc includes becoming pregnant and ultimately killing Ryuji during a confrontation after he regains consciousness. Following his death, she is arrested and confesses her love for him. An alternate storyline within *Night Shift Nurses Kranke* depicts her marrying Ryuji, moving to the countryside, and becoming his devoted wife.

In the sequel *Yakin Byoutou Ni*, Ren's past profoundly impacts Dr. Souichiro Kuwabara, who fell in love with her during his training and obsessively searches hospitals for her. Reuniting at Sei-Katorea General Hospital (also identified as St. Cattleya Hospital), Kuwabara discovers her transformed state under Ryuji's influence. Her emotional detachment and photographic evidence of her exploitation drive Kuwabara to insanity and violent behavior.