Ōka Midarezaki leads the operations department of the Supernatural Phenomenon Treatment Bureau. Orphaned at age three with no memory of his early life or biological family, he was raised by the Bureau and conditioned to avoid emotional attachments, initially claiming an inability to love. Forcibly assigned to head "Operation Cozy Family," a government initiative to prevent apocalypse by reforming the prophesied "Child of Enka," he enters an arranged marriage with Kyōka Midarezaki and adopts multiple non-human children as potential heirs of the destruction god Enka.

His duties require maintaining family cohesion while monitoring the children: Ginka (a cross-dressing former yakuza), Yūka (a survivor of ritual abuse), Teika (a talking lion), Hyōka (a biomechanical weapon), and Gekka (an extraterrestrial jellyfish deity). Despite his initial emotional reserve and pragmatic demeanor, Ōka gradually develops genuine affection and loyalty toward this makeshift family. He openly expresses treasuring Kyōka, causing her visible embarrassment, and later acknowledges evolving romantic feelings for her. His commitment faces constant testing through absurd and dangerous situations, from confronting alien suitors to navigating internal Bureau conflicts. Under extreme duress, he exhibits a tendency to draw a concealed handgun—once even directing it toward himself—revealing the psychological toll of his responsibilities.

Ōka's arc traces his transformation from detached bureaucrat to dedicated family protector. He consistently prioritizes the family's safety, intervening in crises like dehydration tactics against an amorous alien or participating in elaborate schemes to ensure household stability. His pragmatic leadership and deepening emotional investment culminate in a steadfast refusal to sacrifice any family member, symbolizing his rejection of his emotionally suppressed upbringing and full embrace of paternal responsibility.