Hiroyuki Okura is a high school student harboring romantic feelings for his teacher, Kasumi Miyamori. Upon learning that Kasumi and her sister Kaho struggle under crushing debt inherited from their late father, he proposes a solution: he will clear their financial obligations in exchange for both sisters submitting to him sexually. This agreement establishes Okura as their creditor, binding them to serve as his personal sex slaves until the debt is repaid. The arrangement forces the sisters into compliance to escape their financial ruin.

Okura's background centers on his status as a student wielding monetary influence to manipulate the sisters, specifically exploiting his existing infatuation with Kasumi. His actions ignite the narrative's core conflict, casting him as the architect of the sisters' plight. The character undergoes no substantive development, with no deeper examination of his motivations, history, or the repercussions of his conduct. He appears solely within this role, undepicted in any other official media extensions.