Being a fan of Sailor Moon for over 20 years now, I feel like I’ve seen almost all the merchandise that came from the anime and manga. However, I was fairly surprised to learn three years ago, that Sailor Moon had some "secret" books that wasn’t really common knowledge. The books I’m referring to, are the "himitsu" books published by Kodansha for the Sailor Moon anime. Not many people know about these two books, but they are mass produced and aren’t really that rare.
"Himitsu" means secret, so its definitely amusing that not many fans know about these two books’ existance. Here is the reason why so few people know about these volumes: It is common knowledge to fans that Kodansha published short hard-cover childrens’ books during Sailor Moon’s run on TV. These hard-cover books are made of board, and have no more than a few pages summarizing the storyline of the anime. Some fans collect these hard-cover books, but most fans do not because they are made to be simplified for pre-school-aged kids.