Kouichi Hayama serves as the central male protagonist and Suzuna Kuraki's arranged fiancé, residing at the Kuraki estate to prepare for the esoteric Shinto Tsukimachi ceremony central to the family's traditions. His past remains fractured due to an unexplained childhood illness causing complete amnesia, erasing memories of his parents and history before the estate. Fragmented details indicate he lost his step-parents in a traffic accident, prompting a break from university studies for their funerals. During this time, a mysterious yet familiar young woman appeared in recurring dreams, her identity obscured by his memory loss.

A distinct elongated scar marks his chest. Before arriving at the Kuraki estate, he suffered from prosopagnosia specific to female faces, rendering him unable to recognize or remember women's appearances; this condition resolved after entering the household. He exhibits a reserved demeanor yet frequently clashes with Suzuna, suggesting a complex tsundere dynamic, and is depicted as a frequent smoker.

His relationships extend beyond Suzuna. He shares a past connection with Chikako Sawaguchi, a psychology professor visiting the estate due to sensed paranormal activity, identified as his former teacher. Within the household, he interacts with figures like Yuriko Kuraki, the family matriarch who exerts influence over supernatural forces, and Gohei Harukawa, the estate landscaper assisting Yuriko with ritual preparations. His presence intertwines with a mysterious paranormal energy affecting residents, causing increasingly strange behaviors and complicating the ritual. This energy appears linked to the estate's history and the hidden truth behind his own origins.

His journey centers on gradually uncovering his lost memories and true origins, intertwined with resolving the supernatural mysteries surrounding the Kuraki family, their rituals, and the estate itself. This involves confronting manifestations of the paranormal curse alongside other inhabitants.