The cultural significance of 本子 (běnzi) lies entirely in its dual meaning, which represents a fascinating split between mainstream language and niche subculture jargon. The slang usage is directly borrowed from Japanese ACG culture. In Japan, fan-made comics are called “同人誌” (dōjinshi). The “同人” part refers to a group of people with the same interests, and “誌” means publication. Chinese fans, heavily influenced by Japanese anime and manga, created their own terminology. While the formal term is 同人志 (tóngrénzhì), the community adopted the much simpler and more discreet term 本子 (běnzi), literally a “little book,” as a code word. Comparing this to Western culture, the concept is similar to “fanfiction” or “zines.” However, 本子 specifically refers to a visual medium (a comic or art book) rather than written text like fanfiction. Furthermore, while not all 本子 are pornographic, the term has a much stronger association with adult (R-18 or “hentai”) content than the general English term “fan comic.” This makes it a discreet way for fans to search for and discuss this type of content online without being explicit. Understanding this term is a window into the huge and influential 二次元 (èr cì yuán), or “2D world” subculture in modern China.
How you use or interpret 本子 depends entirely on the situation.
In any normal, day-to-day context—school, university, the office, a stationery store—本子 means notebook. It's an extremely common, neutral, and informal word. You use it just like you would use “notebook” or “pad” in English.
This meaning is confined to specific contexts, primarily online and among fans of ACG content.