Ten years after the great calamity, siblings Kiriko and her younger brother Haruki were orphaned and eventually taken in at the Funayama Orphanage. To support the orphans, Kiriko became a street racer, risking her life to bring in funding. During one such race, a Man-Eater appeared and attacked the participants. Haruki attempted to fight it, but was gravely injured. Acting on instinct, Kiriko tried to rescue him, managing only to free his torso and head before being fatally shot in the head.

A doctor, confronted with the imminent deaths of both siblings, performed an experimental procedure, transplanting Haruki’s brain into Kiriko’s body. When Haruki awoke, now inhabiting his sister’s body, he was left in confusion and spent four months in recovery. This event occurred five years prior to the beginning of the story. To reconcile his dual identity, he adopted the name Kiruko, blending both of their names as a reminder that they remained connected.

Over time, Kiruko began working as a traveling bodyguard before eventually opening a handyman office in Nakano. During her jobs, she fought against Man-Eaters and was later commissioned by Mikura Manaka to escort Maru to the mysterious location known as “Heaven.” Alongside Maru, she also pursued her own mission: to find the doctor who performed the transplant and to seek out Robin Inazaki, her late sister’s mentor whom Haruki had once admired.

As their journey continued, Maru confessed his attraction to Kiruko. In response, she revealed the truth of her identity as Haruki but allowed Maru to continue addressing her as “sis,” admitting she had grown used to it. With time, Kiruko began to experience flashes of Kiriko’s memories, which reassured her that her sister’s presence still lived within her. These moments helped her grow more comfortable with herself and embrace her identity.

Kiruko is portrayed as a young adult woman with brown eyes, brown hair, and thick black eyebrows. Her usual attire consists of a modified white USAF MA-1 bomber jacket with purple and blue hemming, worn over a round-neck black shirt. She pairs this with low-rise, form-fitting blue jeans equipped with a holster on her right side, along with light brown high-top sneakers. The bomber jacket was originally a gift from Robin Inazaki during her time as Haruki, making it one of her most cherished possessions.

Following the transplant surgery, Kiruko’s appearance changed noticeably. Her originally black hair grew back brown, and she bears several scars as reminders of the procedure. A circular scar runs around her head from the surgical stitches, while the back of her head hides the bullet wound that nearly killed her. Additionally, her body carries scars across her shoulders, hips, and arms. Kiruko herself describes her hair as dry with a reddish tint, further reflecting the physical transformations brought about by her past trauma.

Kiruko is depicted as lively and approachable, often lightening tense moments with humor. She forms an easy bond with Maru, frequently joking with him and displaying a playful dynamic that resembles the camaraderie of close male friendships. Despite her cheerful outlook, she remains practical and resourceful, able to salvage useful items from debris and maintain composure in the midst of combat.

She is also marked by moments of insecurity and self-doubt. Kiruko struggles with an underlying fear of abandonment, shaped by her past experiences of loss, and often underestimates her own abilities. She tends to misjudge her value to others, questioning whether she is truly useful. However, her confidence grows over time particularly after Maru reassures her of her importance helping her begin to embrace her strengths and trust in her own skills.

Maru
Kiruko cares deeply for Maru, accompanying him on his journey to reach “Heaven” not only out of obligation but also out of personal concern for his well-being. Their bond grows throughout their travels, with Kiruko displaying visible distress when Maru goes missing and pleading with him not to leave her again. While Maru’s combat skills have often saved them, these moments occasionally make Kiruko feel inadequate in her role as his bodyguard. However, Maru frequently reassures her by praising her marksmanship and recognizing her unique strengths. Their companionship is built on mutual reliance and genuine affection. Maru eventually confesses his romantic feelings for Kiruko, but she gently rejects him, unable to reciprocate despite caring for him deeply.

Robin Inazaki
During her childhood at the Asakusa race track, Kiruko admired Robin as a mentor and father figure. Believing he was still alive after her surgery, she set out to find him, using her mission with Maru as an opportunity to reunite with him. However, her admiration was shattered after the events of Chapter 32 (Episode 12 in the anime), when Robin captured her, subjected her to assault, and inflicted deep psychological trauma by forcing “Haruki” to endure the violation of his sister’s body. Though Maru later rescued her, the incident left Kiruko questioning her identity and sense of self. Afterward, she destroyed a photograph of Haruki and Robin together, symbolizing her severed trust. Despite this, when Maru attempted to kill Robin in retaliation, Kiruko stopped him, refusing to allow Maru to become a murderer on her behalf.

The Doctor
Kiruko initially harbored resentment toward the doctor who performed the transplant surgery, striking him upon their reunion in Chapter 53. She accused him of using Kiriko’s body without consent, but he explained that Kiriko had been rendered brain-dead by a gunshot and that he acted in an attempt to save at least one of the siblings. Understanding his intentions, Kiruko realized he had not been malicious, and she eventually apologized for misjudging him.

Marksmanship
Kiruko is an accomplished sharpshooter, praised by Maru for her accuracy. She has demonstrated the ability to dispatch threats with precision, such as killing a charging bear with a single well-placed shot.

Perception
She is a tactical fighter with sharp analytical skills, capable of quickly assessing enemy abilities and identifying ways to exploit their weaknesses. This allows her to adapt efficiently in combat situations.

Navigation
Kiruko is highly skilled in navigation and cartography, able to gather and organize information to chart effective routes for herself and Maru. She reads maps and uses a compass with ease, often compensating for Maru’s struggles in this area.

Resourcefulness
She consistently demonstrates ingenuity in survival scenarios, such as fashioning a makeshift raft to cross a large body of water. Kiruko excels at scavenging useful items from debris, has basic cooking skills, and can quickly gather information through observation, reading, or conversing with locals.

Kiru-Beam
Kiruko carries a specialized energy weapon known as the Kiru-Beam. The gun is capable of disintegrating nearby objects with concentrated blasts of energy. However, its use is limited, as it can only be fired four times consecutively before requiring a recharge. Although somewhat unreliable, the Kiru-Beam has repeatedly proven invaluable, saving both Kiruko and Maru during life-threatening encounters.

Flashlight
Kiruko also uses a portable Nanogrid lamp produced by Biolite. This flashlight is a practical survival tool, aiding her and Maru in navigating dark or unsafe environments during their travels.