TV-Series
Description
Sakae Ashiya possessed the innate childhood ability to see and influence yōkai, making him the only family member with this power. His family was killed by a group of yōkai, leaving him the sole survivor and instilling deep resentment toward them, whom he blamed for causing misfortune.

During high school, Sakae attended the same school as Nara Ashiya, a year above him. He exorcised a yōkai possessing Nara in the school infirmary, warning her that staying would make her feel more "tired," leading to their first meeting where she noted his striking golden hair and eyes. Rumors labeled him the "God of Death" due to unexplained illnesses and accidents befalling those near him, causing others to avoid him. He later secretly joined the Mononokean while still wearing his gakuran school uniform. After joining, he ceased using his influence to kill yōkai, shifting away from his hostility.

As an adult, Sakae married Nara and had two children, Hanae and an unnamed daughter. He occasionally acted oddly by muttering or nodding to himself, later understood as interactions with yōkai. He secretly used his influence to alleviate Nara's illnesses without revealing his abilities. His family believed he abandoned them, unaware of his true fate. He once rescued the yōkai Tōgen after hearing her whispers for help when she was buried in an avalanche's snow, urging her not to disappear.

Sakae died 16 years before the main story on November 2nd. His death occurred while attempting to cure the Mononokean's master, Aoi, of a parasitic shrub infection by transferring his influence. This suppressed the parasite but caused Sakae's body to vanish accidentally. Aoi later attempted to transfer Sakae's residual influence to Hanae, resulting in the son inheriting only half. Aoi's records symbolized Sakae as a cat, describing his death as "watching a cat die." Three years after his death, Aoi disguised herself as Sakae and visited the Ashiya family on Christmas Eve, briefly interacting with a young Hanae who mistook him for Santa Claus.

Sakae's consciousness persisted within Hanae due to their shared influence. When Hanae was mentally overwhelmed by the yōkai Sasa, Sakae manifested in his subconscious, warning that unchecked power use would get Hanae killed. He then possessed Hanae's body to confront Sasa. Noticing Hanae's eyes turning gold during the possession, Sasa questioned why an "ordinary human" had such eyes; Sakae replied, "Unfortunately, I'm no ordinary human," before exorcising Sasa completely. This mirrored Sakae sealing Sasa in a shrine centuries earlier, deeming him untrustworthy. During this possession, Sakae appeared in his younger, high-school-era form. After exorcising Sasa, he briefly conversed with Haruitsuki Abeno, vaguely confirming his role in the sealing before losing consciousness.

Sakae's legacy included 209 documented collaborations with Aoi in the Mononokean's records, represented by cat drawings. His official "disappearance" was recorded in the underworld's calendar as night 48, cycle 27, volume 11, during job number 143.