Kosuna, whose real name is Taiko Koizumi, is a young me rcenary who appears in the anime Desert Punk. Her nickname, meaning litttle sand, reflects her small stature and role as a junior figure in the harsh wasteland. Before becoming Desert Punk's apprentice, she served as the assistant of a sniper known as the Shimmer Sniper, who sought to gain fame by hunting down the infamous Desert Punk. When Desert Punk defeats her master and leaves him humiliated, Kosuna immediately abandons him and begs to become Desert Punk's own student. She convinces him by showing him a picture of a woman with a large bust, claiming it is her mother, and promising that she will develop a similar figure in a few years. Driven by his own perverted hopes, Desert Punk reluctantly accepts her.

Kkosuna's main motivation is to become the number one power babe of the desert, a goal she defines as being stronger than any man and more beautiful than any woman. She begins the story as a naive and somewhat helpless girl, often unable to complete tasks on her own. Despite this initial weakness, she gradually proves to be a surprisingly capable assistant to Desert Punk, learning the tricks of the handyman trade and adopting her mentor's pragmatic, if cynical, worldview. Desert Punk frequently teases her about her flat chest, a source of deep insecurity for her that makes her resent women with large breasts.

In the story, Kosuna serves as Desert Punk's loyal apprentice, accompanying him on many jobs and missions. Their relationship is a complex mix of genuine mentorship and exploitation. While Desert Punk treats her harshly and uses her for his own ends, he also teaches her the survival skills necessary in the desert. She, in turn, looks up to him despite his many flaws and sometimes disapproves of his more ruthless actions, such as when he kills a business partner's children. Over time, her character develops from a dependent girl into a more independent and hardened mercenary. She eventually leaves Desert Punk's side to pursue her own path, and after he is believed to be dead, she takes his place as a wandering handyman and even acquires her own apprentice.

Kosuna's key relationships beyond her master include brief encounters with the scheming mercenary Junko Asagiri, for whom she holds a grudge after being betrayed. She also interacts with the Machine Gun Brothers and other denizens of the desert. In terms of abilities, Kosuna initially lacks combat experience but grows more proficient with weapons. She obtains a powerful new automatic weapon after a brush with death, and she later becomes skilled enough to survive on her own and take on contracts. Her development is marked by a gradual shift from youthful idealism toward the hardened pragmatism needed to survive in the lawless desert.