Astrias is a young, ambitious, and highly skilled warrior who serves as a key antagonist in the early conflicts of Guin Saga. He holds the title of Viscount within the military forces of Mongaul, having inherited his position from his father, Marquis Marx Astrias. Known for his dark hair, dark eyes, and tall stature, he has earned the formidable nickname the Red Lion of Gora due to his prowess and fearsome reputation on the battlefield. Despite his youth, being only twenty years old, he is already famous and considered a formidable captain, having participated in countless skirmishes and large-scale wars.

Astrias is defined by his deep and unwavering devotion to Lady Amnelis, the powerful and ambitious noblewoman of Mongaul. He is a young knight who is completely infatuated with her, serving her with a passionate and unquestioning loyalty. This devotion is a primary motivator for his actions, as he seeks to prove himself and carry out her will. However, beneath his stoic and disciplined exterior as a celebrated captain lies a more volatile and prideful nature. He is prone to intense emotions, most notably a burning fury and deep-seated shame when he is bested in combat. He experiences significant humiliation and anger upon being defeated by the protagonist, Guin, a loss that leaves a lasting scar on his pride. His perspective on warfare is also notable for its philosophical depth; he views battles as living, untamable wild beasts that require both a firm hand and careful understanding, a belief that sets him apart from his commanding officers.

Within the story, Astrias functions as a primary field commander for the Mongauli forces, directly involved in the invasion of the Kingdom of Parros and the pursuit of its escaped royal twins, Rinda and Remus. His role frequently puts him into direct conflict with the series' main protagonist, Guin, and the twins' party. His character undergoes notable development through a series of setbacks and humiliations. After being easily defeated by Guin in a one-on-one duel at Nosferas, he becomes consumed by the desire for redemption and revenge. He also becomes entangled in the larger political machinations of the series, such as being captured and interrogated for information about the twins by the minstrel Marius. Later, he participates in a plot to assassinate the character Naris, believing he has succeeded, only to find himself captured and removed from the immediate conflict, hinting at a potentially longer, uncertain path ahead for him.

In terms of abilities, Astrias is a formidable and experienced combatant. He is a renowned swordsman, as his nickname the Red Lion of Gora attests. His extensive battle experience grants him a sharp tactical mind, and he possesses a unique, almost instinctual understanding of the flow of combat, likening battles to living beasts that must be carefully managed. He is a capable leader of men, commanding respect and fear from his soldiers, though his youth and emotional nature can sometimes be a liability beneath his imposing exterior.