Hiroaki Sakata is a nineteen-year-old young man from Japan who was summoned to another world to serve as a hero for the Huguenot ducal faction, a group that has fled from the Kingdom of Beltram. Before his summoning, he was a ronin, a student who had failed his university entrance examinations, and he spent his subsequent time absorbed in light novels and video games about heroes in other worlds. This background heavily influences his outlook, as he becomes intoxicated by his new special status and fundamentally does not wish to return to his original world, seeing his role as a hero as a form of personal vindication.

Personality-wise, Hiroaki is characterized by an extremely strong desire for self-display and a boastful nature. He easily gets carried away when flattered, which makes him highly susceptible to manipulation by those who know how to appeal to his ego, such as the nobles Duke Huguenot and Roanna Fontaine, often serving as an unwitting political pawn. He has an open disdain for people he perceives as winners in life, including the wealthy and the handsome, and cannot tolerate anyone who steals the spotlight from him. His insecurities in genuine combat or strategic situations are masked by his tendency to belittle those around him. This behavior, coupled with a lack of tact, earns him a poor reputation, especially among perceptive women like Liselotte Cretia and her maid Aria, who see through his superficial charm. He has a temperament typical of an otaku, having personally named his divine weapon "Yamata no Orochi" and harboring a frivolous admiration for the princess knight Sylvie.

Hiroaki's role in the story is primarily that of a rival figure and a deconstruction of the summoned hero archetype. He is positioned as a hero for the Restoration faction but is often more of a liability than an asset. He is deeply jealous of the protagonist, Rio, who is also known as Amakawa Haruto. This jealousy stems from Rio's superior combat abilities, his numerous feats, and the company of beautiful women that surrounds him. This envy drives Hiroaki to challenge Rio to a duel, a match in which he is utterly defeated despite wielding the powerful water-controlling sword, Yamata no Orochi. During the fight, his inability to control his own power causes collateral damage, leading to a severe reprimand from Princess Christina Beltram and a period of disciplinary confinement.

Key relationships define much of his narrative. He is closely guided and manipulated by Stewart Huguenot and Roanna Fontaine, who direct his political actions for their own benefit. His relationships with women are often transactional and colored by his ego. He was initially engaged to Flora Beltram and Roanna Fontaine, but his feelings cool considerably after Flora is rescued by Rio, and he agrees to a political marriage with Princess Rosalie of the Galarc Kingdom instead. A persistent subplot involves his failed attempts to secure a marriage with Liselotte Cretia, who firmly and repeatedly rejects him. His disdain for those he considers rivals also extends to other knights, such as Alphonse Rodan, who privately derides him as an all-talk, frustrating individual. Later in the story, he finds some companionship and emotional stability with his fellow countrymen, Saiki Rei and Murakumo Kouta, whom he appoints as his personal assistants, and together they pursue a passion for writing stories.

In terms of development, Hiroaki begins as a quintessential paper tiger, full of grand boasts but quick to cower in fear during real battle, such as when his group was attacked by monsters. However, following significant defeats, particularly his humiliating loss to Rio and a subsequent defeat by another hero named Renji, he shows signs of growth. These failures shake his delusions and motivate him to take his training more seriously. While he remains far less skilled than other heroes, his attitude begins to shift; for instance, when the new hero Masato is introduced, Hiroaki's usual braggadocio is notably absent, a change observed by Satsuki Sumeragi.

Regarding his abilities, Hiroaki possesses a divine weapon, a sword he has named Yamata no Orochi, which grants him the power to manipulate water and provides a significant boost to his physical strength and speed. While the weapon's power is tremendous, Hiroaki's own combat skills are lacking. He has not undergone proper training, a situation partly orchestrated by Duke Huguenot to prevent him from becoming too powerful and rebellious. As a result, his fighting style relies on overwhelming force rather than technique. This lack of control and experience makes his power "awesome, but impractical" in a serious fight against a seasoned warrior like Rio or the antagonist Reiss Vulfe, who was able to incapacitate him with a single blow.