Jonathan is a shinigami, or death god, who appears in the narrative as a replacement partner for the character Izumi after Meroko departs from that role. His visual appearance is marked by a top hat, and he has a distinctive habit of often speaking in English. Initially presented in this capacity, his demeanor and true motivations undergo a significant shift as the story progresses.

His primary role evolves from that of a fellow shinigami to an active antagonist. Jonathan reveals to the protagonist Mitsuki a painful truth: the shinigami were aware that her beloved childhood friend, Eichi, had already died. This revelation sets him on a more fanatical path, and he eventually becomes a direct threat, attempting to harm Fullmoon, the alter ego of Mitsuki, as well as her friends. This turn defines his function in the narrative as a source of conflict and danger that the main characters must face.

Key relationships are central to understanding his position. He becomes the partner to Izumi, stepping into a role previously held by Meroko. His actions directly put him into opposition with Mitsuki, also known as Fullmoon, and her circle of allies. His development is characterized by a clear descent from a supporting supernatural figure into a fanatical antagonist driven by his own agenda regarding the shinigami's rules and the fate of humans. Regarding specific personal history, abilities beyond the standard traits of a shinigami, or deeper insight into his internal motivations beyond his fanaticism, no reliable direct information exists.