Tonari no Oneesan ga Hentai de Doushiyou!?

When his father departs for a few days to work offsite, young Jun is left in the care of Chisato, the college-aged woman living next door. For some time, he has harbored a quiet fascination with her, and this unexpected sleepover grants him the opportunity to spend the night in her home. What begins as a routine arrangement quickly shifts when Jun gains firsthand access to her private bedroom, uncovering a side of his older neighbor he never anticipated. During his stay, Jun stumbles upon a peculiar toy among Chisato's belongings. Driven by youthful curiosity, he finds himself entirely unsure of its purpose or how it functions. Rather than dismissing his questions or hiding the object away, Chisato takes an unexpectedly forward approach to the situation. She decides to personally guide him, offering to teach him exactly how the strange device works. This impromptu lesson transforms a simple overnight visit into an eye-opening experience for the boy, as his long-standing interest in the girl next door leads him into unfamiliar territory under her direct instruction.