Hiro Kinashi, also known by the nickname Retro, is a recurring character and competitive karuta player within the series. He is a student of similar age to the main cast and is notably tall with a slender, pale complexion. He has a distinctive bowl-cut hairstyle and short black hair, and his eyes are almost always shut, making their color unknown. His nickname in the original Japanese is Hyoro, which means lanky, a direct reference to his physique, while the localized name Retro is used in English adaptations.

In terms of personality, Hiro is highly competitive and possesses a strategic mind. He is described as being correct in his plays approximately eighty percent of the time. He is known for a unique method where he relies on a set of his own prominent cards, referred to as his Retrot Cards, to determine his team's fate, treating the cards almost like a fortune-telling device. Despite this practice, he is not superstitiously bound by them and has been known to defy their prediction to prove his team's strength. He is sensitive about his nickname, consistently asking others to call him by his given name, Hiro, whenever they refer to him as Retro. After becoming the president of the Hokuo Academy Karuta Club, he struggles personally to achieve Class A ranking, a goal that his own club members do not expect him to reach. Despite this, he takes his leadership role seriously, personally recruiting all new freshmen players and diligently nurturing even the untalented new recruits to help them improve.

Hiro's primary motivation is tied to his pride in his team and his desire to prove the strength of the Hokuo Academy Karuta Club. He takes on a difficult but crucial role in team competitions. While he does not hold the position of captain in these team games, he strategically chooses to play against the opposing team's strongest ace players. He does this to give his own teammates a better chance of winning their matches, sacrificing his personal odds for the good of the club.

Within the story, Hiro is initially presented as a rival to the Mizusawa Karuta Club. However, after his team loses to them, he gains a deep respect for them and becomes a consistent supporter of Chihaya Ayase in particular. He has known Chihaya, a fellow karuta player, longer than most others, though they have rarely faced each other directly in a match. He hypothesizes that this is because Chihaya prefers to play against opponents she considers strong. He sees both Taichi Mashima and Arata Wataya as his rivals in karuta, with Arata being his eternal rival. He maintains a generally good relationship with Akihito Sudo, although he finds Sudo's intense pressure tactics uncomfortable and has described him as a sadist. He also showed concern for Taichi when Taichi left the Mizusawa Karuta Club, stating a preference that he remain around.

Hiro's development is marked by his assumption of the presidency of his school's karuta club, a position he takes over from a senior member. This added responsibility highlights his dedication to the club and its members, even as he personally finds advancement difficult. His abilities as a player are defined by his strategic understanding of the game and his unique system centered on his Retrot cards, a portmanteau of his nickname and tarot cards. This method demonstrates his analytical approach to the sport, as he uses it to plan his team's strategy and preemptively decide the flow of a match.