Masahito Karikiri presides as the chief priest of the Nitto Shrine on Hitogashima Island and leads the Karikiri family, guardians of the island's rituals. He cultivates a gentle, approachable public image, though he is known for his tendency toward lengthy conversations and a fondness for video games, especially RPGs and simulation titles from his youth. His true identity is Shidehiko Hishigata, a centuries-old hybrid of human and shadow, founder of the Hishigata clan. Shinpei Ajiro exposes his ageless nature by confronting him with photographic proof placing him on the island 70 and 40 years prior. His origin stems from witnessing Haine, the shadow entity Hiruko, consume the original Karikiri. Becoming Haine's consort, he fathered a child with her and adopted the "Karikiri" surname to position himself as the husband of a deity. He achieved immortality by manipulating Haine into repeatedly copying his consciousness and memories into new clones across 300 years, transferring his existence into younger bodies to sustain his youth. During the 1732 famine, he orchestrated the transformation of islanders into shadows to conserve resources, believing this preserved the island's population. In his shadow form, known as Shide, he manifests as a muscular black humanoid with four arms and four eyes, a stark contrast to his human disguise: a tall, bespectacled man in priestly attire. He serves as Haine's primary enforcer, advancing her goal of reviving Hiruko, while his true motive exploits her power to secure his own eternal life. His personality blends superficial politeness with profound cruelty and sadism. He relishes the suffering of others, particularly Shinpei's, and sheds his friendly demeanor instantly upon exposure. He demonstrates strategic cunning, analyzing time-loop mechanics to counter Shinpei's abilities, and exploits malleable black mud armor formed from former shadows in combat. Across multiple time loops, he engages the protagonists directly. He murders Shinpei's parents after they discover Hiruko's cave and attempt to reveal it. In later loops, he battles Hizuru Minakata and Ryūnosuke, adapts to repeated resets by anticipating opponents' tactics, and meets defeat when Ushio severs his connection to the shadow armor, rendering him vulnerable to Mio's attack.