Jubei Kibagami is a wandering mercenary ninja in feudal Japan, known for his exceptional swordsmanship and pragmatic approach to survival. His past is marked by tragedy, having been forced to kill members of his own ninja clan, the Yamashiro, in an event that has left him a drifter with a deep-seated distrust of authority and large organizations. He once worked for the Tokugawa government, but that experience reinforced his desire to remain a masterless ronin or wandering vagabond, free from the schemes of those in power.

In terms of personality, Jubei presents a laid-back, snarky, and sometimes jovial exterior, but this masks a firm and unshakeable moral code. He admits to working for money, yet he is remarkably disinterested in wealth, often accepting far less than a job is worth if his clients are poor. A core part of his character is a deep respect for life and self-worth; he openly states that he hates people who think little of their own value, a principle that drives his interactions with others. This honor is most famously demonstrated when he refuses to sleep with a female companion, Kagero, to cure himself of a lethal poison because he recognizes she is in a distressed state and refuses to take advantage of her. Despite his cynical and sometimes flirtatious nature, he is fundamentally a chivalrous and principled individual.

Jubei is primarily motivated by a combination of survival, a desire for a quiet life, and a personal sense of justice. While he often tries to avoid getting involved in large conflicts, he is consistently drawn into battles against powerful supernatural enemies, such as the Eight Devils of Kimon, a group of demonic ninja. His role in the story is that of an anti-hero who gets caught up in a conspiracy, where he is often blackmailed or coerced into service by the cunning government spy, Dakuan. Despite his protests, he becomes the reluctant protector of others, most notably the poison-using ninja Kagero and the Light Maiden Shigure, a guardian of a sacred relic.

His key relationships are central to his development. His dynamic with Dakuan is one of constant friction and grudging mutual respect; Dakuan represents the ruthless government pragmatism that Jubei despises. His bond with Kagero is more significant, as it breaks through his cynical shell. Through her, he reveals his capacity for genuine care and vulnerability, acting not just as a warrior but as a protector who encourages her to value her own life. The death of someone he cares about serves as a powerful catalyst, pushing him beyond mere survival to a quest for vengeance against his greatest nemesis, Genma Himuro, a demonic lord from his past.

As a combatant, Jubei is classified as a "Badass Normal," possessing no inherent supernatural powers like his enemies. Instead, he relies on peak human physical conditioning, incredible speed, and masterful skill. His most notable technique is the "vacuum blade," a sword slash so fast and powerful it creates a cutting shockwave capable of striking distant foes. He is a pragmatic fighter who uses his wits to exploit the weaknesses of superhuman opponents, such as attacking the unstoneable eyes of a rock monster or using an enemy's own bees against them. He also employs various ninja tools, including a hidden throwing dagger, a length of wire attached to his sword hilt for retrieval or trapping, and exceptional physical senses that allow him to detect ambushes and poisons. Over the course of his journeys, his development is subtle but noticeable, moving from a man who only wants to be left alone to one who actively accepts his role as a protector, even wearing the headband of a fallen comrade as a tragic keepsake.