Kyouko Sonoyama serves as a librarian at a college, overseeing part-time assistants Takumi and Tamura. She maintains a reserved, occasionally strict professional facade, yet Takumi senses a hidden passionate intensity beneath her controlled exterior. This duality connects to her secret role in the clandestine "Midnight Sleazy Train" organization, where she operates as an initiator under the leadership of her college superior. With this superior, Kyouko engages in a sadomasochistic dynamic, adopting a submissive stance that starkly contrasts her workplace persona. Despite recognizing the risks, she covertly observes Takumi through camera surveillance and ultimately initiates a relationship with him, revealing her inability to suppress her impulses toward him.