Ninya is a silver ranked adventurer who served as the magic caster and strategist of the adventurer party known as the Swords of Darkness, based in the city of E-Rantel. Ninya's primary aspiration was to obtain one of the legendary swords of darkness, but this goal was secondary to the more urgent personal mission of finding their older sister, who had been taken by a noble during Ninya's childhood. This event left a deep impression on Ninya, fostering a strong sense of resentment toward the nobility. As a former villager who became orphaned at a young age, Ninya survived by relying on this sister, and the loss of her drove Ninya to become a stronger adventurer out of dedication to bringing her back.

Ninya cultivated a humble and good-natured personality within the party, earning a reputation as a reliable and capable member. Despite an outwardly gentle demeanor, Ninya harbored a deep hatred for nobles, stemming from the trauma of losing a family member to their cruelty. It is later revealed that Ninya was actually a woman who had been disguising herself as a man, likely for safety or practical reasons while adventuring. This disguise extended to choosing to be addressed with male pronouns by the party. Ninya's older sister was named Tsuareninya.

In terms of abilities, Ninya was considered a prodigy among magic users, possessing a natural aptitude for magic that allowed learning and mastering spells in roughly half the time it would take an ordinary mage. This talent earned Ninya the nickname the Spellcaster, though Ninya preferred not to be called that out of embarrassment. Ninya had already achieved the ability to cast second-tier spells at a young age, which was uncommon in the New World. Ninya's magical talent, combined with a separate aptitude for magical learning, made the character a highly valued member of the Swords of Darkness and a notable figure among the lower-ranked adventurer community.

Ninya's role in the story is primarily as a supporting character within the early arcs of the series, interacting with the main characters during their time in E-Rantel. The Swords of Darkness encountered Momon and Nabe, and Ninya later accompanied the party on a mission that led to a confrontation with the rogue adventurer Clementine. During this confrontation, Ninya was killed by Clementine, and the death was a pivotal moment that underscored the threat posed by the stronger figures in the New World. Ninya never fulfilled the goal of finding Tsuareninya, as she was lost before that reunion could occur. The character's development is cut short by this premature death, leaving the personal narrative unresolved. Ninya's relationships within the party were close, particularly with fellow members Peter, Lukrut, and Dyne, and the party shared a strong sense of camaraderie. Ninya had no direct connection to the main antagonist organization, the Great Tomb of Nazarick, and was unaware of the true nature of Momon and the forces that would later reshape the world.