D'Altania Charles, often called Nia by those close to her, is a tall, blonde-haired young woman who originally comes from France and transfers to Buou Academy. She is a unique figure in this setting as a foreign samurai, a master of a distinctive combat style that employs two large claymore swords used as dual blades.

Nia’s personality is marked by a deep and enduring capacity for affection, even in the face of profound betrayal. She meets Yoshihiko Tokugawa while she is practicing origami, and a romantic relationship begins to develop between them. However, this bond is shattered when Yoshihiko uses her as an unwitting test subject, injecting her with a genome to artificially transform her into a master samurai, a type of enhanced warrior known as a sword princess. Despite this cruel exploitation, Nia continues to harbor genuine feelings for Yoshihiko, a loyalty that defines much of her role in the story.

As a result of Yoshihiko's actions, Nia becomes bound to him in a master-servant relationship, which forces her to act as an assassin for the Tokugawa faction. This compulsion leads her to attack the dojo of her potential allies, acting against her own will. Her defining moment comes when she sacrifices her life to protect Yoshihiko from falling rubble. In her final moments, she clings to an origami samurai helmet that Yoshihiko had given her in the past, a token of their happier time together.

Her death serves as a catalyst for Yoshihiko, who realizes his true feelings for her. Using his awakened power as a shogun, he revives her with a kiss. This act of resurrection transforms Nia, allowing her to become a true master samurai, marked by a concentrate seal appearing on her left hand. Through this event, her character completes a development from a victim of circumstance to a genuinely empowered warrior, her bond with Yoshihiko finally affirmed and reciprocated.