Sylvie van Hossen, formally Sylvia van Hossen, is a noble from the fictional Flemish Principality in Eastern Europe. As the elder daughter of Vincent van Hossen, head of the van Hossen family, she has a younger sister, Maria, who actively supports her relationship with Teppei Arima. Her mother passed away when she was young, shortly after Maria's birth, deeply affecting Sylvia; despite profound grief, she was unable to cry at the funeral, reflecting her struggle with emotional expression. Physically, Sylvia possesses a slender, curvaceous figure, standing 168 cm tall with measurements of 88-57-87 cm. She has long blond hair typically styled in a bun, violet eyes that may appear gray in certain lighting, and distinctive thick eyebrows. Her attire frequently includes European-style plate armor featuring breastplates, pauldrons, greaves, and heel-like sabatons during combat or formal duties, complemented by a signature rapier. In civilian settings, she wears school uniforms or elegant outfits such as strapless dresses and skirt suits. Characterized by high standards and bluntness, Sylvia initially displays outward repulsion toward her arranged fiancé, Teppei Arima. She struggles to articulate feelings verbally, preferring actions over words—a trait stemming from her stoic upbringing and reinforced by her military role as captain of the Flemish cavalry unit, the Horse Riders. Beneath her reserved exterior, she is honorable, hot-blooded, and deeply loyal, especially to her childhood best friend Charlotte Hazelrink, the Princess of Hazelrink. Her relationship with Teppei evolves from competitive sparring partners to romantic partners; their fencing matches, which she typically wins by narrow margins, symbolize their dynamic. Though initially resistant to the engagement, she gradually acknowledges her feelings, culminating in a kiss in Episode 11 of the anime and eventual marriage with pregnancy in the visual novel's conclusion. Her development across media involves confronting emotional vulnerability. In the original visual novel, she reconciles her duty with personal desire, marrying Teppei and expressing profound happiness upon becoming pregnant. In the adult-oriented OVA, she engages in a pre-battle intimate encounter with Teppei before leaving to defend her principality, entrusting her maid Yuu to care for him in her absence—a departure from her typically restrained demeanor. Sylvia's cultural identity blends Flemish traditions with extensive education in Japan, though she spends little of her adult life in her homeland. Her Dutch-German heritage is suggested through linguistic and naming conventions in flashbacks.