Jaken is a diminutive, imp-like demon who serves as the unwavering retainer to Sesshōmaru, the powerful dog daiyōkai. His background reveals that he was once the ruler of his own imp tribe in the Musashi Province. Decades before the main events, his tribe was attacked by a powerful yōkai, and many of his people were slaughtered. Sesshōmaru appeared and destroyed the demon, saving Jaken’s life. Instantly captivated by Sesshōmaru’s immense strength, Jaken pledged an oath of loyalty and abandoned his position to follow him. In return for this service, Sesshōmaru granted Jaken the Staff of Two Heads, a weapon that would become his primary tool.

Personality-wise, Jaken is defined by his extreme and vocal loyalty to Sesshōmaru. His entire existence revolves around serving his master, whom he constantly praises. He acts as though he has absolute confidence in Sesshōmaru’s every action and is never surprised by his successes. However, this facade often cracks on the rare occasions when Sesshōmaru struggles in battle, causing Jaken to panic, a contradiction that others, particularly Rin, are quick to point out. He is also notably cowardly and self-preserving, as his own demonic power is very weak. Much like the flea demon Myōga, Jaken often looks for excuses to leave dangerous battlefields, believing his survival instincts are more important than fighting. Despite this cowardice, he possesses a surprisingly broad and deep knowledge of demonic lore and history, though he delivers his explanations in a condescending manner that leads few to take him seriously.

Jaken’s primary motivation is to serve Sesshōmaru and, ideally, to see him establish an empire where Jaken could become the Chief Minister. He is driven by a deep-seated gratitude and admiration for his master’s power, and he seeks Sesshōmaru’s approval in all things. While his duties often involve performing lesser errands and acting as a caretaker, he takes great pride in being the chosen servant of such a powerful lord. His role in the story is that of a confidant, messenger, and comic relief. He frequently explains Sesshōmaru’s thoughts or the nature of various spiritual items and enemies to the audience and other characters. He is also entrusted with the crucial task of looking after the human girl Rin, who travels with them, and often the two-headed dragon A-Un.

His key relationships are central to his character. His bond with Sesshōmaru is absolute; he is fiercely loyal and terrified of disappointing his master. Sesshōmaru, for his part, seems to tolerate Jaken and, on rare occasions, demonstrates a measure of care for him, such as when he used the Tenseiga to resurrect Jaken after he was killed by the swordsmith Kaijinbō. Jaken’s relationship with Rin is more complex. He initially finds her presence annoying, as she is a vulnerable human child who complicates their travels. However, he becomes her reluctant caretaker and often puts himself in harm’s way to protect her, less out of fondness and more out of fear of what Sesshōmaru would do if he failed in his duty. He also has a bickering rivalry with the young fox demon Shippō, with whom he constantly trades insults.

Over the course of the story, and particularly in The Final Act, Jaken undergoes subtle but noticeable development. While his cowardice and self-serving nature remain, he becomes more responsible, especially concerning Rin and Kohaku. When Sesshōmaru decides it is too dangerous for them, Jaken is for once reluctant to obey and stay behind, wanting to follow his master into the final battle. His most significant moment of growth comes when he believes Rin cannot be saved and bursts into tears, showing a genuine emotional attachment to the girl he once considered a burden.

Notable abilities of Jaken are almost entirely tied to his weapon, the Staff of Two Heads (Nintōjō). This staff, which bears the faces of an old man and a woman, has several functions. Its most common use is as a flamethrower; the old man’s face can spew powerful flames capable of incinerating human soldiers and weaker demons. It also has a detection ability, which was originally used to search for the Black Pearl that led to Sesshōmaru’s father’s grave. In the sequel series, he is also shown using the staff to create barriers. Beyond his use of the staff, Jaken has few innate demonic abilities. He ages very slowly, has heightened senses, and can project a demonic aura, but it is extremely weak, and his physical strength is comparable to or even less than that of an ordinary human.