For a project I am working on, I visited the Shochiku Otani Library for the first time since it moved into the new building. It used to be located in the old Shochiku headquarters, which were even further down Harumi-dori from the Kabuki-za and the Shine Patosu. Shochiku, suffering through hard times at the end of the nineties, sold the land to the ad company ADK, which redeveloped it and now Shochiku rents some space in the new building for the Otani Library. The Shochiku headquarters are now across the street above the Togeki Theater. You can see the front of the ADK Shochiku Square building with a sign for the Library in the photo below.
The Library is focused primarily on theater and film (remember, Shochiku, the studio that gave us Ozu, Kinoshita, and Tora-san, is also a theatrical company, owning the Kabuki-za and a number of other kabuki and legit theaters). The main reason to go there is to view the scripts for theatrical and film productions, especially those of Shochiku. In some cases, they have not only several generations of the script of a single film, but also the press book, theater programs, stills and the poster. This is the place to come if you are studying a Shochiku film (though they have materials on other studio films as well).
What it does not have much of, unfortunately, is internal studio documents, which are essential for understanding not only how the company works, but the corporate happenings behind the production of a specific film. Most Japanese studios treat these either as secret documents or they throw them away.
A couple of years ago, Tasogawa Hiroshi wrote a book on the making of Tora Tora Tora entitled Kurosawa Akira vs. Hariuddo, which won several awards in Japan. Everyone praised it, but forgot to mention the irony that it only could be written because US studios donated all these internal documents to archives. Little of such important research can be done in Japan.
The other problem with the Otani Library--although this is a problem shared by most Japanese archives--is that they have become overly protective of copyright, usually under pressure from the major studios. Don't expect to photocopy a full script here. Don't expect to use any of the stills here (you have to get permission from the studio, which in most cases will not make a distinction between a commercial book and a research article--it will still ask you to pay a couple hundred dollars). I've written this before in several places, but the recent over-protection of copyright--and the lack of insight to promote fair use or scholarly research--is strangling film studies, if not also film culture, in Japan.
Update: The book I was researching at the time has come out: Research Guide to Japanese Film Studies.