Kisaragi Saemon is a shinobi from the Kouga Manjidani clan. He is the older brother of Okoi, a fellow ninja from the same clan. As one of the ten chosen representatives of his clan, Saemon is forced into a deadly conflict against the rival Iga clan. His place in this war is defined by his extraordinary skills in espionage and a deep personal tragedy that fuels his actions.

By nature, Saemon is a cool, aloof, and complex individual who carries out his duties with a professional sense of detachment. He is able to transition between the violence of war and moments of peace without outward emotion. This reserved exterior hides a very human interior, as he does not take pleasure in the killing that his duty requires. After dispatching an enemy, he consistently offers an apology to his slain opponent, expressing a hope that in death they might find the peace they were denied in life. The only person who pierces this icy shell is his sister, Okoi, to whom he shows genuine affection and a protective, almost overbearing, concern. His bond with her is deep, and he is shown to be a surprisingly cheerful soul in her presence.

Initially, Saemon is not deeply invested in the clan war, but the brutal capture and death of Okoi at the hands of the Iga transforms him completely. Following her death, Saemon throws himself entirely into the conflict, viewing victory for his clan and revenge for his sister as one and the same purpose. To achieve this end, he becomes willing to use any method, whether physical or psychological, to break the remaining Iga shinobi. His role in the story shifts from a supporting spy to a primary agent of retribution, actively hunting down the enemies of Kouga.

Within his own clan, Saemon has key relationships beyond his sister. He appears to be close friends with Gyoubu Kasumi and Kagero, working effectively alongside them in combat. He also shares a deep enmity with Hotarubi of the Iga clan, a hatred that stems from Saemon's involvement in the death of her beloved Yashamaru and Hotarubi's own brutal attack on his comrade, Shougen. This animosity escalates when Saemon, disguised as Yashamaru, uses a moment of affection to attack Hotarubi, an act that horrifies her and leads to a violent confrontation between them. His relationship with Nenki Mino is also marked by extreme hatred, as Nenki was responsible for killing his sister, an act for which Saemon shows no forgiveness even after Nenki's own death.

Saemon's development is a tragic arc from a composed and detached observer to a grieving brother consumed by a quest for vengeance. This path is exemplified in a pivotal scene where, disguised as the Iga ninja Yashamaru, he holds his dying sister Okoi, maintaining a calm facade to have a final, heartbreaking conversation with her. From that moment forward, he discards any remaining passivity, becoming a relentless and resourceful foe who uses his unique abilities to dismantle his enemies one by one.

His most notable ability is a powerful form of disguise. By pressing a person's face into soft earth or clay to create a mold, Saemon can then reshape his own face to perfectly match theirs. Combined with a talent for mimicking voices, this makes him a master of impersonation and infiltration. However, this technique is purely cosmetic; it does not grant him the memories, fighting styles, or any other special abilities of the person he is copying. Furthermore, the disguise can be seen through by animals or individuals with heightened senses. Beyond his espionage skills, Saemon is also a highly capable hand-to-hand combatant. He has demonstrated the ability to defend himself against multiple opponents simultaneously and dispatch enemies with precise and devastating efficiency, such as instantly snapping an adversary's arm. While his talents are not suited for direct confrontation, his strategic use of disguise makes him an exceptionally dangerous support ninja, directly contributing to the deaths of several Iga clan members.