Ren Nanase

Bright and friendly, Ren Nanase is a 22-two-year-old nurse at the St. Juliana Hospital who is arguably the most iconic character of the series. She is the first nurse Ryuji meets and the first who genuinely welcomes him as a friend and superior. When her love for an inpatient boxer, Naoya Ohkawa, is discovered, Ryuji learns of her match fixing and uses it as blackmail. Like the nurses to come, in spite of the abhorrent treatment she receives, Ren develops Stockholm syndrome and becomes emotionally attached to her abuser. Ren is distinguishable by her incredibly long hair, of which is usually tied into a ponytail.

(Source: Wikipedia)