Kage Mushi-sama

Mika Koizumi is a high school girl born into a family with an ancient pact. In exchange for prosperity, the daughters of the Koizumi family are offered as human sacrifices to a non-human entity known as 'Kage Mushi-sama' (Lord Shadow Bug). Mika accepts her fate, believing she was born for this purpose. The entity manifests as a mass of tentacles that constantly demands her body, even at school. She uses the nurse's office to hide while the entity violates her, enduring the relentless and overwhelming pleasure as part of her duty.