Oka Myojin is a shrine maiden of the Myojin family, destined to protect the world from Oni who prey on humans through possession. Born the youngest daughter in Aichi Prefecture, she underwent the generational Shikizakura ritual as a child, a tradition tied to sealing Oni, which left her severely cursed. Her sheltered upbringing resulted in unfamiliarity with worldly affairs and common technology like smartphones.

She possesses long dark hair (later shortened to medium length), pale blue eyes, and a slim build. Her typical attire includes a blue hairband, a white long-sleeved shirt, and either a blue skirt or red hakama as her miko garments. She utilizes Kagura suzu ritual bells in her duties.

Oka's personality blends determination with cheerfulness. She maintains a calm demeanor, rarely showing strong emotions, yet exhibits intense focus during her shrine maiden responsibilities. She values peaceful activities with friends but remains resolute against Oni. Her sheltered life contributes to occasional naivety, balanced by deep loyalty and protective instincts, especially toward her older sister Benio.

Her supernatural heritage grants her abilities: performing exorcisms, conducting the Shikizakura ritual, possessing enhanced human capabilities, and purifying Yoroi powered suits to prepare them for combat. She supports fighters by enhancing their Yoroi with her powers for effective battles.

Her story begins when she encounters high school student Kakeru Miwa during an Oni attack. After he accidentally dons a Yoroi and saves her, she purifies his suit and integrates him into her team. Alongside allies like Ryo Hattori, Kaede Naruse, and Haruko Yamada, she undertakes missions across the Tokai region to protect humans. Key developments include confronting her worsening curse, discovering her father Masanori Myojin is the demon unleashing chaos in Japan, and uniting her team to defeat him. Following his downfall, she enters a peaceful new life with her companions, ensuring past tragedies do not recur.

Relationships define her journey. She shares a close bond with her older sister Benio, who dotes on her though Oka offers limited reciprocation. She develops romantic feelings for Kakeru and maintains supportive friendships within her team. Allies such as Ukon Kijima and Issa Inuzuka assist her sister's separate anti-Oni efforts.