Safu is characterized by her directness, blunt honesty, and strong-willed nature. She speaks her mind without hesitation and is unafraid of confrontation, as demonstrated in her willingness to stand up for herself during disputes, such as in the episode Drenched Rat. Her assertive personality sets her apart from many other residents of No.6, who are more reserved or conditioned by societal norms.

Like Shion at the beginning of the series, Safu occasionally struggles with expressing her emotions in socially conventional ways. Rather than confessing her romantic feelings for Shion directly, she approaches the subject with clinical detachment at one point requesting his sperm as a way of preserving his genetic legacy, which highlights both her intellect and emotional awkwardness.

Despite her forthright demeanor, Safu is deeply affectionate and loyal. She cares profoundly for Shion and shows unwavering commitment to those she loves. Her emotional strength is matched by her bravery; she ultimately chooses to sacrifice herself in order to aid Shion and Nezumi in exposing the truth behind No.6. In her final moments, Safu reflects on the pain of losing everything she held dear, but remains resolute in her choice, embodying both selflessness and courage.

Safu is a teenage girl with chin-length dark brown hair and matching brown eyes. Her typical outfit consists of a white jacket worn over a pink turtleneck shirt, complemented by a pink scarf. She also wears a red skirt, black tights, and brown boots, presenting a neat and modest appearance reflective of her practical personality.

In her childhood, Safu was known for wearing what others considered “outdated” clothing, often donning handmade sweaters knitted by her grandmother. These garments, while old-fashioned, reflected her close familial bond and simpler upbringing within the highly structured society of No.6.

Safu is introduced as a highly intelligent and emotionally forthright girl living in the elite city of No.6. At age twelve, she gives a presentation in class, only to be mocked by her peers for wearing outdated clothes hand-knitted by her grandmother. Enraged, she lashes out at one of the students but is quickly restrained. In the manga adaptation, Shion comforts her by telling her that the sweater suits her personality, making her blush as she thanks him for being the first to say something kind about it. From early on, it is clear that Shion is the most important person in her life.

In the anime, Shion is invited to Safu’s home to celebrate his birthday. She gifts him a sweater identical to hers, but dyed purple in honor of his name, which is derived from the purple shion flower. During this visit, Safu proudly shows off her wardrobe entirely handmade by her grandmother demonstrating both pride in her roots and affection for Shion. Before he leaves, she insists on giving him a personal birthday gift. Without warning, she kisses him on the cheek, subtly revealing her feelings. Naively, Shion compares it to the way his mother kisses him, and before Safu can clarify, they are both distracted by the rare sound of the Moon Drop “crying.”

A time skip follows, and both characters are now sixteen. Safu reunites with Shion at a shop, having been away attending a prestigious boarding school in No.5. Their conversation is lighthearted until Safu brings up the past and questions what happened to him at age twelve. Shion dodges the topic, prompting Safu to steer the conversation toward her imminent departure. Blushing, she makes an unexpected request asking for Shion’s sperm, citing genetic compatibility. Shion, flustered, tries to respond, but she quickly retracts the request, admitting she simply wants to be with him. When Shion tells her he only sees her as a friend, she becomes frustrated and starts to walk away. However, before parting, Shion tells her to wait two years promising that when she returns, he will grant her wish. Encouraged, Safu vows to study hard so that no other boy will look at her.

Tragedy strikes when Safu is forced to return to No.6 after the death of her grandmother. At the airport, she confides in an elderly stranger about her doubts regarding the city. Visiting the retirement home, she becomes suspicious about her grandmother’s death and attempts to contact Shion only to discover he is missing and considered a criminal. She then visits Karan, Shion’s mother, who confirms Shion’s whereabouts in the West Block and reveals the corruption within No.6. Safu decides to leave and search for him, despite Karan’s pleas to stay safe. Tearfully, she confesses her love for Shion, and Karan, moved by her honesty, shares what she knows—including the name of Shion’s companion, Nezumi.

Unbeknownst to her, Safu has been under surveillance by the Security Bureau. Upon leaving the bakery, she is captured and taken to the Correctional Facility, where she is imprisoned in a water-filled containment tube and labeled as a “Sample.” Terrified and helpless, she mentally calls out to Shion, begging him to save her.

In a poignant mental flashback, Safu imagines walking through a forest with Shion, delighting in the beauty of nature and the simplicity of their conversation. She reacts with innocent joy to sights like squirrels and beech nuts, unfamiliar with these natural elements. As the dream continues, she tries to express her feelings, asking Shion if he’s happy when he’s with her. In her mind, she envisions Shion calling her his most important person, a final fantasy reflecting her unspoken hopes.

In her final inner monologue, as her consciousness begins to fade, Safu reflects on the person she truly loves and wants to see. Her thoughts return to Shion affirming that, even at the end, he is the one who matters most to her.

Safu is exceptionally intelligent and was enrolled in the same Special Curriculum as Shion within the elite educational system of No.6. Her academic focus is physiology, in which she demonstrates a high level of expertise. Her scientific mindset is often reflected in her straightforward approach to problems and her tendency to analyze situations logically. Though not a combatant, her intelligence, critical thinking, and educational background make her a valuable figure in the narrative, particularly in contrast to the rigid and conformist nature of No.6’s society.

Shion
Safu and Shion have been close friends since childhood, having grown up and attended school together within the elite districts of No.6. Their bond is characterized by a strong emotional connection and deep mutual understanding. On Shion’s 12th birthday, Safu baked him a cake and gifted him a hand-knitted sweater made by her grandmother an identical design to her own, but in purple to reflect Shion’s name, which is derived from the purple shion flower.

Safu, who specializes in physiology, knows Shion well enough to read his emotions even when he attempts to conceal them. For instance, when she asks if he’s jealous of her continued elite status, Shion replies yes, but Safu quickly sees through his answer and determines it’s not true. Her ability to analyze both people and situations sets her apart from many of her peers.

Over time, Safu develops romantic feelings for Shion. Before leaving for her two-year study abroad in No.5, she confesses her desire to be with him framing it first through a scientific lens by pointing out their compatible genetics, but ultimately admitting her emotional longing. Shion, taken aback, replies that he only sees her as a dear friend and is not ready for such a relationship. However, he asks her to wait two years and promises that he will give her a proper answer then. Safu agrees, though she teasingly remarks that Shion still has much to learn.

Nezumi
Safu’s first encounter with Nezumi is indirect during her final moments with Shion before departing for boarding school, she notices a change in his behavior when he is distracted by a voice in the distance. Though she does not realize it at the time, the voice belongs to Nezumi. Safu later reflects on this moment, recognizing it as the first time she had seen Shion respond to someone so intensely, hinting at the emotional shift Nezumi would bring into his life.