"Poison Pink" Vinsmoke Reiju is the eldest child and only daughter of the Vinsmoke Family, making her both the princess of the Germa Kingdom and a commander in its military arm, Germa 66. Reiju is a slim young woman with shoulder-length hair that covers her right eye and curls upwards at the roots. Like her siblings, she has curly eyebrows. Reiju's overall facial features strongly resemble those of her deceased mother, but she also resembles her brother Sanji enough that Luffy initially mistook her for him, until Chopper pointed out that she is female. Both of her thighs are tattooed with a number '6'.
When commanding the forces of Germa 66, Reiju wears a dark dress with a split in the center going down to her stomach, and covered by target-shaped symbols - references to the number '0' (Rei) in her name. She wears dark gloves, a pair of headphones with the number '66' on them, and a patterned cloak shaped like the wings of a moth. When not dressed in her Germa 66 gear, Reiju has been shown wearing a skinny headband in her hair, and a short, satiny dress with a frilled neckline and a cravat. For formal functions, she also wears a dark, thigh-length royal cape that is clasped in front of her neck. As a child, Reiju had shorter hair, but wore a similar dark headband. She has been shown wearing a light dress with the letter "Z" on the right side, as well as other light dresses featuring the number "0" in various forms. She also occasionally wore a dark ascot. Unlike her cruel and abusive brothers, Reiju is kind and empathetic - especially towards her brother Sanji, although this is frequently masked by a cool, callous demeanor. As a child, Reiju would openly laugh at Sanji's misery as he was enduring his brothers' vicious acts of cruelty, although she would treat him with care and sympathy when they were not around. While Sanji retains a vivid memory of his elder sister's amusement at the abuse he suffered as a child, Reiju confided to him that she only laughed with their brothers to avoid being subjected to similar cruel bullying herself. She also treated Sanji's wounds and seemed to express concern for him when it was said that he had died (but hid her concern behind a smile). She even cried in secret as she listened to their father cast Sanji out of the family, and she queried why Sanji would ever return to a place that had provided him with so few happy memories.
Furthermore, although she stated she was not on his side, it was she who helped Sanji escape his imprisonment as a child and encouraged him to find friends on the sea. To this day, Reiju is the only member of Sanji's family (excluding his deceased mother) to treat him with any degree of compassion. She is also very civil. Upon first meeting Luffy's Sanji retrieval team, Reiju apologized to them for Yonji's rudeness, and thanked them for everything the Straw Hats had done for her younger brother, Sanji. Her occasional actions and her general manner of speech are also quite flirtatious towards men, similar to Sanji's flirtatious behaviour towards women. Even before she was properly introduced to Luffy, she unabashedly placed her mouth over his in order to suck out the poison which was festering throughout his body. Reiju enjoys her luxurious lifestyle and is somewhat dismissive about the possible pleasures of living as a non-royal, as she fails to understand why Sanji would renounce the privileges of being a prince and choose a "mundane" pirating life instead. Despite her intelligence and kinder nature, she seems to only extend her kindness if it is convenient to herself. She shows kindness when it is easy for her to do so and get away with it, but is unwilling to risk her own safety and comfort for the sake of others. The very notion of someone putting others before themselves is so alien to her that she seems to be literally incapable of understanding why someone would value the safety and happiness of others above themselves. This puts her at odds with Sanji, as she could not understand why he would return to a home that abuses him just for the sake of protecting his mentor. Like the rest of her family, she has high regard for strength, pointing to the strength of the Vinsmoke Family throughout the generations, and all the achievements and privileges that they have obtained as a result of exercising that strength. Reiju has exhibited a calculating side; for example, she appears to be aware of Sanji's weakness for attractive women, showing him ten beautiful chambermaids that would be at his beck and call in order to convince him to accept his arranged marriage. She also easily charmed the Sanji retrieval team in their first meeting, humiliating Yonji and apologizing for his behavior in order to prevent a confrontation with the Straw Hats. She also appears to be naturally introspective, pondering the merits of war against a protracted failed peace. She is often shown musing silently to herself as she watches certain developments unfold, and frequently hides or disguises her true thoughts and feelings.