Ryuu has short, messy brown hair and striking aqua blue eyes, which stand out against his typically modest attire. He is usually seen wearing baggy, age-appropriate casual clothing, often paired with his signature scarf. His usual wardrobe includes knickerbockers with fitted cuffs, black stockings or hose, and puffed boots, reflecting both comfort and practicality suitable for his work in the Royal Pharmacy.

After relocating to Lilias, Ryuu frequently wears the lined winter poncho gifted to him by Garak Gazelt, providing warmth in the colder climate and marking his place among the pharmacy staff there.

In Chapter 108, Ryuu debuts a new haircut, having trimmed his hair into a shorter style. He explains that he chose to cut it because he thought it would be easier to manage, reflecting his practical and no-nonsense approach to daily life.

Ryuu is known for his mature, calm, and somewhat apathetic personality, which often causes others to treat him more like an adult than a child or to feel uncertain about how to approach him. His exceptional intelligence and early involvement in complex pharmaceutical work create a noticeable distance between him and his peers. While not intentionally cold, Ryuu can struggle to empathize with others’ emotions and is often confused by strong emotional reactions, which in turn makes social interaction difficult for him.

This emotional detachment, combined with his interest in poisons and toxicology, has led to misunderstandings and rumors about him in the capital. Many people feel unsettled by his quiet, intense presence, making it hard for him to form close connections. Ryuu himself feels uncomfortable with being treated like an adult all the time, and as a result, did not make many friends growing up.

Since he was brought to the palace at a young age, Ryuu had little opportunity to socialize with children his age, often isolating himself in his office and devoting long hours to his work. He rarely engaged in play or physical activity, and he has admitted on several occasions that he wishes to “grow up soon” a reflection of his desire to become someone more reliable, trustworthy, and resilient, both mentally and physically.

Over time, particularly after relocating to Lilias, Ryuu begins to open up and adapt to a more social environment. Surrounded by other pharmacists, he slowly learns how to communicate more naturally and understand the feelings of those around him. He becomes more observant and careful in his interactions and begins forming genuine friendships. Although he remains quiet by nature, Ryuu gradually becomes less awkward and more expressive, showing growth not just in his professional life but in his ability to connect with others on a personal level.

At a young age, Ryuu was brought to the capital of Clarines due to his reputation as a prodigy in herbal medicine. Recognized for his exceptional knowledge and natural aptitude, he was admitted into the Royal Pharmacy despite his age. When Shirayuki passed the palace pharmacist entrance exam, Ryuu personally requested her as his apprentice, marking the beginning of their close partnership.

In Chapter 5, Ryuu is shown gathering herbs with Shirayuki and explaining his passion for pharmacology, particularly his interest in how poisonous plants interact. Upon their return, a man visits the pharmacy requesting medicine, only to insult Ryuu afterward for his blunt attitude. Shirayuki, angered by the disrespect, defends Ryuu, prompting the man to retract his comment. Ryuu, however, overhears the exchange and tells Shirayuki that such criticism isn’t worth getting upset over highlighting his calm and composed nature.

During the Lilias Arc, Ryuu accompanies Shirayuki to Lilias as part of their training under Chief Pharmacist Garak. Amidst a widespread illness caused by the Olin Maris plant, Ryuu meets Kirito, a boy around his age who brings several children to the pharmacy for treatment. The two quickly form a close friendship, marking a rare moment of connection for Ryuu, who had often struggled socially.

After their initial return to the capital, Ryuu and Shirayuki are sent back to Lilias on a new assignment to study the Olin Maris further, with a goal to develop a safe version of the plant that retains its luminous properties. Before their departure, Ryuu is summoned by Prince Izana, who reveals plans to relocate Ryuu to Wilant Castle once his research is completed, recognizing his growing importance and skill.

During their second stay in Lilias, Ryuu reveals to Shirayuki and Obi that he’s been experiencing joint pain. It is later revealed to be a sign that he is undergoing a growth spurt, a change that becomes evident at the end of the 10-month time skip. In Chapter 91, Zen, Shirayuki, and Obi encounter Ryuu, Kirito, and Lata while taking shelter from heavy rain. Zen is visibly surprised by how much Ryuu has grown, both physically and socially.

Following the successful development of the non-toxic Olin Maris variant, now renamed Phostyrias, Ryuu and Shirayuki receive their next assignments from Garak. Shirayuki is ordered to remain in Lilias to help propagate the new plant, while Ryuu is instructed to return to the capital in three months a decision that takes him by surprise. However, choosing his own path, Ryuu expresses his wish to remain in Lilias and join Shirayuki and Obi in their journey to spread Phostyrias across Wilant, further solidifying his role as a trusted and capable young pharmacist.

Shirayuki
Ryuu chose Shirayuki as his apprentice not only because of her skill and dedication, but also because her red hair reminded him of the Yura Shigure plant his favorite, due to its vibrant color. Despite being technically her senior, Ryuu asked Shirayuki not to address him with any honorifics, as he found it strange for an adult to use them toward a child. Over time, Ryuu gradually opened up to Shirayuki, forming a deep and trusting bond with her. Their relationship resembles that of siblings, with Shirayuki often caring for Ryuu like an older sister. Ryuu clearly admires and cares for her; for instance, when he noticed Shirayuki crying over Zen’s log book, he immediately informed Zen Wistaria, showing his concern for her emotional well-being.

Obi
Due to his role as Shirayuki’s bodyguard, Obi frequently spends time with Ryuu, and over time, the two develop a close friendship. Obi affectionately teases Ryuu with nicknames like “Half Pint,” “Little Ryuu,” and “Ryuu-bou” (Ryuu-boy). Their interactions are often playful, with Obi occasionally giving Ryuu piggyback rides. When Ryuu mentioned that his joints were aching, Obi immediately picked him up to confirm his suspicion—that Ryuu was undergoing a growth spurt, showcasing their growing familiarity and Obi’s protective instincts.

Garak Gazelt
Garak, the Head Royal Pharmacist, is both Ryuu’s mentor and guardian. Since Ryuu’s arrival in Wistal, Garak has played a crucial role in raising and educating him, treating him with the care of a mother figure. While their relationship is primarily that of teacher and student, it has a strong familial quality, as Garak looks after Ryuu’s health, growth, and emotional development. Her concern for his well-being goes beyond the workplace; she even sends Ryuu to Lilias for field experience, believing it would help him develop socially and broaden his horizons, despite him being one of her most promising young pharmacists. In Chapter 57, Ryuu expresses heartfelt gratitude toward her, a moment that nearly brought Garak to tears, highlighting their deep mutual respect and affection.

Kirito
Kirito is Ryuu’s only friend close to his age and someone who complements him with a completely opposite personality. While Ryuu is quiet, introverted, and serious, Kirito is loud, cheerful, emotional, and full of energy. Their friendship begins when Kirito brings a group of sick children to the pharmacy in Lilias, and he quickly grows to admire Ryuu’s knowledge and composure. Despite Ryuu’s social awkwardness, Kirito’s outgoing nature helps break the ice, leading to a genuine friendship that brings Ryuu out of his shell and teaches him how to better connect with others.

Zen Wistaria
Zen is one of the few people who treats Ryuu as a child, acknowledging his youth without undermining his intelligence or abilities. Ryuu is comfortable around Zen, trusting him enough to share his insecurities, particularly his difficulty in reading other people’s emotions. Zen shows a special fondness for Ryuu, and during the events in Lyrias, when asked if he wanted to experience anything in the city, he revealed that seeing Ryuu was what he looked forward to the most. Upon reuniting with him after a long time, Zen was shocked at how much Ryuu had grown, further reflecting the bond and sense of pride Zen feels toward him.