Ballard Kurofune stands as one of the most enigmatic and pivotal figures within his narrative, often recognized as the first Meros Warrior to appear and a direct source of inspiration for the protagonist. His origins are steeped in tragedy and loss; he is portrayed as the sole survivor of a forgotten world, a time before Monsters became the absolute rulers of reality. He belonged to an ancient lineage of courageous fighters known as the Meros Warriors, who once defended humanity against these supernatural threats. This past casts him as a living relic, a wanderer from a bygone era of open warfare, now adrift in a society that has been secretly enslaved and has largely forgotten the true nature of the monsters that demand periodic child sacrifices.

Kurofune's personality is defined by a deep-seated solitude and a weary, almost melancholic charisma. He lives as a vagabond, moving from town to town with no permanent attachments, his existence solely focused on a single-minded pursuit. While he is a legendary and highly skilled warrior, he is not driven by a desire to save all of humanity in a broad sense. Instead, his motivations are intensely personal and obsessive: he is locked in a relentless, lifelong quest to destroy a specific adversary he has sworn to eliminate at any cost. This enemy is Hor, a monster with whom Kurofune shares a uniquely complex and cruel bond. Their relationship transcends that of simple hunter and prey, possessing a dark intimacy that suggests they are inseparably linked, almost as two sides of the same coin.

Within the story's progression, Kurofune serves as a critical catalyst for the main character, Bocca Serenade. When his Ivermachine, a multifunctional motorcycle-like device, is damaged in battle, Kurofune arrives in Bocca's town for repairs. Recognizing a latent potential in the young student, Kurofune takes it upon himself to reveal the suppressed truth about the great war of the 20th century that led to the monsters' rise. He becomes a mentor figure, demonstrating the reality of the Meros Warriors' fight against creatures like Hor, who demands child sacrifices. After this initial encounter and battle, Kurofune disappears, prompting Bocca and the female thief Sayoko Tsukinomori—who owes Kurofune a debt for saving her from Hor—to vow to find him.

The culmination of Kurofune's personal war leads him to Hor's monstrous lair, a lost island that never appears in the same place twice. He ventures alone into the labyrinth at the island's core, leaving the real world behind to plunge into the heart of his enemy's madness. This final confrontation transcends normal time; what feels like years to Kurofune within the labyrinth passes as only a few months in the outside world. Here, he manages to trap Hor, but the victory is a pyrrhic one, condemning them both to an endless struggle within that nightmarish space until one of them finally perishes. When Bocca eventually finds him and enters the labyrinth, Kurofune reveals his grim past and the true, tragic nature of his connection to the monster. This act solidifies his role as the archetypal fallen hero, whose desperate solution to a personal vendetta results in a form of eternal imprisonment, passing the torch of the Meros legacy to the next generation.

In terms of abilities and distinctive traits, Kurofune is a formidable combatant. Unlike other warriors who might use a traditional bow, he wields a crossbow. His specific Meros technique is called Ballad, a melody of the heart that serves as his unique form of attack, contrasting with Bocca's Serenade. His Ivermachine is named Jaguar Sun. Visually, he is recognized by his blue eyes, shoulder-length purple hair, and stubble, with his Meros tattoo located on his left arm. His command to activate his Meros arrow is Flush, which is the same command used by Bocca, further emphasizing their connection.