Kaiki is known for his cynical, gloomy disposition and a worldview rooted in nihilism. He believes that nothing in the world is inherently true, with the sole exception of money, which he regards as the only constant something that can replace anything and be replaced itself. As a natural schemer, Kaiki conceals his true thoughts behind a façade of ambiguity. He is highly skilled in deception and manipulation, making his motivations difficult to interpret. He once explained his name by likening “Kai” to a mound of clam shells and “Ki” to a dead tree fitting metaphors for his hollow, lifeless approach to morality.

Kaiki takes pride in the fact that he has no pride. He openly identifies as a conman and imposter, using his reputation as a tool in his elaborate schemes. His conversational style is fluid and adaptive, always adjusting his behavior to best serve his interests. He is unafraid to compromise or retreat when necessary, always seeking to optimize outcomes in his favor.

In Koimonogatari, Kaiki’s inner thoughts are explored in greater depth, revealing a man governed not by ethics but by personal logic and selective morality. While he is habitually dishonest, he follows through on promises provided he finds personal value in doing so. His decisions are often spurred by indirect motivations, such as when he was warned to abandon a job by Izuko Gaen and a mysterious messenger (later revealed to be Hitagi Senjougahara). Rather than being discouraged, Kaiki took the warning as a challenge exactly as Senjougahara had intended.

Though observant and shrewd, Kaiki occasionally overlooks simple truths. For instance, when he found a letter in his hotel room, he assumed a third party had broken in, missing the simpler explanation that it could have been slipped under the door. Similarly, in his attempt to deceive Nadeko Sengoku, Kaiki devised a straightforward lie claiming Koyomi Araragi and his friends had been in a traffic accident to prevent her from killing them. However, knowing Nadeko’s distrustful nature and the near immortality of Araragi, this plan proved ineffective. His failure to consider her psychological state ultimately led to the scheme’s collapse.

Kaiki is a tall, pale middle-aged man with a distinctly gloomy and ominous presence. His typical attire consists of a black funeral-style suit, often accompanied by a loose necktie adorned with a red club symbol at the knot. His facial expression rarely changes, marked by a cold, unsmiling look and eyes that alternate between vacant indifference and unsettling sharpness. His hair is usually slicked back, with two long bangs that hang toward the bridge of his nose.

In Koimonogatari, Kaiki is often seen in a more casual but equally somber outfit a standard trench coat with his hair worn down in a short, unkempt style. One scene notably depicts him taking a cold shower, causing his skin to appear ghostly blue, emphasizing his morbid aesthetic.

In Hanamonogatari, Kaiki returns to his original hairstyle but appears more polished. He is shown sporting a neatly trimmed goatee and a pair of glasses, giving him a slightly more refined, yet still somber, appearance.

Kaiki is a self-proclaimed “fake specialist”, an expert in oddities who, despite his deep understanding of the supernatural, firmly rejects their existence. Instead of addressing real spiritual phenomena, he chooses to exploit the beliefs of others for profit. He operates as a conman, using his extensive knowledge of paranormal lore to deceive those who seek supernatural assistance.

During his college years, Kaiki was a member of the Occult Research Club, where he studied alongside several notable figures in the series, including Meme Oshino, Yozuru Kagenui, Tadatsuru Teori, and Izuko Gaen. This academic environment shaped his understanding of oddities, though it also marked the beginning of his career as a fraud.

Kaiki was the first of five conmen approached by Hitagi Senjougahara during her struggle with a weightlessness curse. Instead of helping, he deceived her father, stole their money, and vanished. This betrayal had lasting consequences, contributing to her parents’ eventual divorce. However, it is later revealed that Kaiki believed Hitagi’s mother was a toxic influence and that removing her from the family was necessary for Hitagi’s future. In his own view, the con was an act of twisted compassion.

Despite his morally questionable methods, Kaiki has connections to the Gaen family. His decision to assist Koyomi Araragi and Senjougahara in Koimonogatari was largely influenced by his indirect involvement with Suruga Kanbaru, the niece of Izuko Gaen. In the past, Kaiki harbored feelings for Suruga’s late mother, Tooe Gaen, and made a personal promise to ensure Suruga’s safety after Tooe’s death. This lingering commitment becomes a rare glimpse into Kaiki’s hidden sense of obligation and sentiment.

Hitagi Senjougahara
Kaiki was the first conman Hitagi approached in her attempt to cure her weightlessness, but he deceived her father, took their money, and offered no help. This betrayal left a deep scar, resulting in Hitagi’s lasting resentment and hostility toward him. However, it is later revealed that Kaiki’s actions were motivated by his belief that removing Hitagi’s mother from her life was ultimately in her best interest. Despite their antagonistic past, Hitagi seeks his help once more in Koimonogatari, leading to a temporary and uneasy alliance.

Koyomi Araragi
Kaiki and Koyomi have a strained relationship, largely shaped by Kaiki’s deceptive nature and Koyomi’s moral opposition to him. Although they are fundamentally at odds, Kaiki shows a grudging respect for Koyomi’s persistence. In Koimonogatari, Kaiki unexpectedly takes on the role of protector for Koyomi and his friends, showing he is capable of acting altruistically under specific circumstances.

Suruga Kanbaru
While Kaiki and Suruga have limited direct interaction, she plays a crucial role in his decision-making. Kaiki agrees to help Hitagi and Koyomi only because it would indirectly protect Suruga. This stems from a past promise Kaiki made to Suruga’s late mother, Tooe Gaen, to look after her daughter.

Tooe Gaen
Kaiki once had romantic feelings for Tooe Gaen, a connection that significantly influences his later decisions. Her death left an emotional mark on him, and his promise to ensure Suruga’s safety serves as a rare example of his personal loyalty and lingering affection.