Istavan is a central character in the anime Guin Saga, introduced as a young and ambitious mercenary. Known by his nickname, the Crimson Mercenary, Istavan is approximately twenty years old and possesses a thin yet strong frame, often described with mischievous obsidian eyes that reflect his cunning and quick-witted nature.

His background is marked by a significant prophecy. Born with a jewel clutched in his hand, a seer predicted that he would one day rule a kingdom and marry the Princess of Light. This prophecy shapes his worldview and ambitions, as he firmly believes that the exiled Princess Rinda of Parros is the destined Princess of Light who will lead him to his throne.

Istavan’s personality is a blend of roguish charm and practical ruthlessness. He is a battle-hardened survivor who initially presents as a mercenary without scruples, yet he is portrayed with a distinct sympathy that makes him a likable rogue. His sense of humor is wild and mischievous; he finds outrageous situations funny and particularly enjoys teasing the serious Princess Rinda. Despite his frequent complaints about danger or difficult tasks, he demonstrates a strong sense of loyalty, especially to the protagonist Guin, whose orders he ultimately follows. He possesses an almost supernatural sixth sense for impending disaster, often disappearing from a location just before a calamity strikes. Underlying his opportunistic exterior is a cheeky, unshakable belief that he will survive any situation, a trait that gives him a unique charm.

In the story, Istavan serves as a key ally to the amnesiac leopard-headed warrior Guin and the twin heirs of Parros, Rinda and Remus. He joins their party early in their flight from the invading Mongaul army, acting as a pragmatic and resourceful companion who often contrasts with Guin’s more noble and straightforward heroism. He is a rogue who provides the group with crucial survival skills, including infiltration and tactical deception.

His motivations are driven largely by self-interest and the prophecy that governs his destiny. He seeks to reclaim the kingdom he believes is his birthright, and his infatuation with Rinda is tied to her perceived role as his key to power. However, his relationships with the main cast show significant development. He forms a deep bond of mutual trust with Guin, who relies on Istavan’s cunning for missions that require subtlety rather than brute force. His dynamic with Rinda evolves from a transactional interest based on prophecy to a more complex personal obsession and respect.

Istavan’s development is significant throughout the series, particularly in the source material. He is a cunning fighter whose notable abilities are less about raw strength and more about intelligence, infiltration, and psychological warfare. In one notable display of his prowess, he infiltrates a massive enemy army by disguising himself as a slain soldier and gains the trust of a high-ranking captain, whom he then leads into a deadly ambush that results in a complete massacre of the enemy troop. This act demonstrates his immense bravery and tactical genius, proving that his cocky demeanor is backed by a steel nerve and lethal competence.

Later in the story's progression, the prophecy comes to pass in a complex manner. He eventually marries Princess Amnelis of Mongaul and becomes a king, fulfilling the first half of the prediction. However, his obsession with Rinda persists, as he is later said to be the cause of her husband's death. The narrative explores his internal struggle, including becoming possessed by an evil spirit that leads to tragic actions, ultimately resulting in his imprisonment after being freed from its control. Despite these darker turns, his role as the resourceful and ambitious Crimson Mercenary remains a cornerstone of the epic's exploration of destiny, ambition, and the gray areas of heroism.