In the 2021 context of Japanese adult media, titles like this often utilize:
The "Shiri Ochi File" series typically follows a voyeuristic or documentary-style format. The central theme of the second volume involves a woman leading a double life. While her boyfriend believes she is a typical, perhaps even conservative partner, the "file" reveals a side of her personality or activities that she keeps strictly hidden from her domestic life. Production Style Shiri Ochi File. 02 Kareshi Ga Shiranai Kanojo... -2021-
To enhance the feeling of a "file" or a secret recording. In the 2021 context of Japanese adult media,
"Kareshi Ga Shiranai Kanojo" (The Girlfriend the Boyfriend Doesn't Know) Thematic Focus: "The Secret Life" perhaps even conservative partner