Kain (架印?) is a young Shirushigami, a Shinigami bookkeeper of Kyoukai, whose main responsibility is to keep track of the lifespan of humans on Earth, so that the Shinigami know when and where they may be needed in order to help the souls of the recently deceased reach the Wheel of Reincarnation. His black cat is Suzu.
Kain has silvery white hair and sharp blue eyes. He is often seen wearing glasses while working in the department.
Kain is a very serious person who cares for his mother, and as such, hates the Damashigami Sabato for using her for money and causing the two to become poor. Because of this, Kain also resents Rinne only for being his son.
As someone who works in Kyoukai, Kain shows little regard for the rules as he attempts to end Rinne's life early, and shows no remorse when an innocent human bystander like Sakura gets caught up in their battle. However, he cannot harm humans or allow humans who aren't ready to die yet to ride the wheel of reincarnation as he would be punished for it.
He also can hardly tolerate shame in many domains, such as his financial status because of his mother's naivete, and being at fault for an incident and having to apologize, especially to Rinne.
He admitted to caring for Renge, stating that it was his dream for her to succeed in life.
Kain was raised by his mother after his parents divorced for unknown reasons. One day, Kain's mother asked if he wanted a new father and takes him to see Sabato, who promised marriage and offered her a pile of junks and stuffs that belonged to Rinne, including his elementary school present, as collateral. Even as young as he was, he knew Sabato was a bad person. While Kain's mother naively believes Sabato to be a good man, her money has provided the financial backing for the Damashigami Company, and as Sabato continuously sent her "love letters" every month which are thinly veiled requests for money, they became broke.
When Kain was in middle school, serving as Student Council President, he was often the object of affection for Shinigami girls including Vice President Renge. However, because of Sabato's leeching, he was unable to pay for the Elite Shinigami High School, and so instead, found a job at the Mortal Census Bureau and became a Shirushigami.
Because no part of his job requires him to take part in field work of any kind, and in order to hide his family's connection to the Damashigami Company, Kain works in secrecy, hunting down Damashigamis and plotting to bring down the rogue Damashigami Company.
At some point, Kain came across Suzu, who was holding a sign saying that she was up for adoption for free, and due to his family's financial status, he took her in as his black cat by contract.
He is first seen trying to locate the Damashigami company through an operation, for the route changes all the time, but Ageha blew it. He then shows up above Rinne, revealing himself to be his creditor to whom Rinne owes payment, because Sabato had left Rinne's name as his co-signer on the loan thereby making Rinne accountable for his father's actions, and stating his debt is so tremendous that he could only be able to pay off with his life span. So he took Rinne’s life flame and his Haori, and forced his friends Sakura, Tsubasa and Ageha to quickly locate the Damashigami company. However, they along with Rokumon follow Rinne’s spirit going to the other world, where they meet Kain’s mother who welcomed them to her mansion. Understanding no one knows the location of the Damashigami company, Kain drugged and locked up Rinne’s friends in the storage room and tried to make Rinne go to the wheel of reincarnation. His friends nevertheless managed to escape and brought Rinne’s elementary school present, which turns out to be a ring of judgment. And the tool proved useful for Rinne precluding Kain to retake Rinne’s life flame, making it clear Rinne is being attacked unjustly, but could not lead anyone to the Damashigami company as Sabato thought of setting a tight security. So Kain admits defeat, but is nevertheless still committed to take on Rinne.
He would cross path with Rinne again many times, mainly while performing certain duties as a Shirushigami or acting on his own, and would seize any opportunity that would be unfavourable to Rinne, but would sometimes cooperate with him for different reasons including arresting Sabato.
He reunites with Renge and often meets her as well, unaware that she too couldn't apply to the Elite Shinigami High School because of Sabato and currently works for his hated Damashigami company, as she tries to hide it from him however she can, going so far as to hit him.
- Shirushigami Scythe: A tool used by all Shirushigami, looking different from the Shinigami Scythes, rather powerful, as it could extract Rinne’s life flame.
- Seizure Talisman (差押 Sashiosae)
- Shinigami Senses
- Scythe Fighting
Kain loves his mother very much. Although he tries to convince her that Sabato is a wrong man, he doesn’t dare to break her heart by telling her that he used her money to found the Damashigami Company.
Kain absolutely hates Sabato, and swore to bring him and his hated company down.
They are not on friendly terms, for Kain considers Rinne as guilty as his father. But since Sabato is his top priority, he would sometimes cooperate with Rinne to bring him down.
She is very loyal to Kain, but as her carefree attitude can be troublesome to him, Kain is often annoyed but puts up with her.
Considering his sister to be an idiot for being the Damashigami President’s assistant, he considers her an idiot as well, and so they are not on friendly terms. Once, when a matchmaker proposed a rich girl to him, he strongly refused, upon learning that it turned out to be her.
Kain has a slowly blossoming connection with Renge, who he has always seen as pure, true and beautiful, ignoring she actually works directly for his hated Damashigami Company. He did hear the rumors that she never took her entrance exam to the Elite Shinigami High School and so became a Damashigami, but would not believe it.
- "As long as you are Rokudo Sabato’s son, as far as I’m concerned, you are equally guilty…" (六道鯖人の息子である以上、ぼくにとってはきさまも同罪。。。) - Chapter 58, after stating he can no longer take Rinne's life flame
- “Pardon my Suzu.” (うちの鈴がすまん) – Whenever she does something bad
- Kain's name is a combination of two characters that mean "support" and "stamp". Possibly related to his desk job within the realm of the afterlife.
- There was a mistake on the covers of volume 6 and 10. On volume 6, Kain's eyes are colored a dark purple while on volume 10 his eyes are an ice blue.
- Kain looks similar to Sesshōmaru from InuYasha.
- Both he and Renge were unable to attend the Elite Shinigami High School because of Sabato, and so became different types of Shinigami.