This is a semi expose style movie of the Japanese AV (Adult Video - their porn) industry. It's not a documentary, but takes on the form of actress' vantage into the industry she works in.
Hiromi, a country girl has dreams of becoming a celebrity in Tokyo, and leaves her home soon after her graduation from high school. She has a dream to be recruited to be an actress in the streets of Tokyo. She finds work at an airport security, but one day her dream comes true, and she gets recruited by an owner of an unknown production company. He recruits her as a "model" but it's actually to be a "nude" model. It's not exactly what Hiromi was looking for, but she can't turn away from the opportunity. She gets a stage name of Mihiro and starts to appear as nude model followed by an appearance in AV movies.
I believe that this is a movie based on semi-autobiographical novel written by none other than Mihiro herself. I've heard of Mihiro, but am not familiar with her works. From what I understand she was a very prolific workaholic in her field, and became one of the most successful AV actor, and nude model of her time. Through her work she's succeeded in becoming a regular actor and TV personality realizing her dream when she was in high school (source en.Wikipedia).
As mentioned, I'm not too familiar with Mihiro's works, and only realized that this is a movie about her because I've heard of her name before. She probably had what it takes to obtain the success she has. Real life Mihiro shows up few times in this movie as well. It's an interesting look into the Japanese porn industry. As usual the Japanese seems to take their jobs deadly seriously, and the producers (at least the ones she's worked with) weren't sleazy at all, but went on with the production of their videos with dedication and professionalism.
For people who aren't familiar with Mihiro, this is rather a slow movie, that doesn't have much ups and downs to its story. How this movie rates for you probably depends a lot on how familiar you are with Mihiro, and how much of a fan of hers you are.