Alka is the central protagonist of the story, a young woman and the last surviving member of the Clan of the Sword, a group of highly skilled assassins. Her background is rooted in tragedy and the rigid discipline of her clan, having been trained from a young age in the arts of combat and assassination. This life left her with a deep-seated loyalty to her clan's code, but it also stripped her of visible emotion, rendering her an extremely reserved and laconic individual who rarely speaks and displays little outward feeling. She is easily identified by a distinctive swallowtail butterfly tattoo on her body, which marks her as a member of her clan and is a known symbol for bounty hunters seeking a reward on her head.

Alka's primary motivation is a quest for revenge. Her master, Hon, was killed by Jin Varrel, a powerful agent of the Palam Empire and a former member of the Clan of the Sword. This singular goal drives her forward, compelling her to hunt down her master's murderer while also being pursued by the empire and others who wish to claim the bounty on her. Her quest for vengeance is not just a personal mission but is also tied to the "Code of the Clan of the Sword," an internal set of principles that governs her actions and her purpose as a warrior.

In the story, Alka acts as a wandering, solitary force whose path crosses with various individuals and communities. Her role is that of an avenger, but she often finds herself entangled in the conflicts of others, such as defending a village from the Palam Empire or being used as bait by a gang of outlaws. Her journey takes her across a fantasy landscape, moving from one episodic encounter to another, where her presence as a deadly assassin inevitably brings violence. Despite her cold exterior, she becomes a catalyst for change and revelation for many she meets, while she herself remains largely detached from the world around her, focused solely on her goal.

Key relationships play a crucial role in her development. She forms a brief but significant bond with Yuu, a fellow student of her master Hon, who shares her quest and ultimately helps her defeat Jin Varrel. Yuu's death is a pivotal moment, causing Alka to scream in agony and experience emotions for the first time. Other important figures include Karen, the proprietress of an inn, whose own hidden past connects her to Alka as a victim of her assassin work; Jin Hazuki, a bounty hunter and alcoholic gunslinger who both hunts and aids Alka; and Dan Loana, the leader of the Pleasure Gang, who seeks to use Alka for her own revenge against the empire. These relationships, often fraught with betrayal and tragedy, force Alka to confront the consequences of her life as a killer.

Alka undergoes significant development from an emotionless, code-driven instrument of revenge to a person burdened by guilt and seeking a new purpose. After killing Jin Varrel, she finds her revenge hollow and is confronted by the suffering she has caused, including the family of a past target. This leads her to reject her life as an assassin, as she realizes she no longer wants to kill. However, her past continues to haunt her, culminating in a confrontation with Karen, who reveals Alka killed her husband. Broken and lost, Alka is forced to wander once more, contemplating the true cost of her actions and the possibility of a life beyond the sword.

As an assassin of the Clan of the Sword, Alka possesses notable abilities centered on immense strength, superhuman agility, and lethal efficiency with a blade. Her fighting style allows her to dispatch multiple armed opponents in rapid succession with precise, deadly strikes. She is highly resilient, able to survive grievous injuries that would be fatal to others, including being struck by a bullet and suffering from a mystical ailment called "Impurity". Her swallowtail butterfly tattoo is suggested to be a talisman that protects her from the full effects of Jin Varrel's Impurity spell, which can tear others apart.