Books at the Wesleyan Library: Use the Library OneSearch or Advanced Search to search the Library Catalog for books (both print and electronic) and other materials in the Wesleyan Library. 
Books Anywhere Else:  Search WorldCat to find books and other materials in other libraries across the world. You can search Worlcat in Japanese.  
Books in Japan:  Use the National Diet Library (総合目録ネットワークシステム 国会図書館).  This union catalog consists of bibliographic databases of the National Diet Library of Japan, some prefectural libraries, and some public libraries in government-designated cities.  Search Webcat Plus.  WebcatPlus is a union catalog of Japanese university libraries and research institutions maintained by the National Institute of Informatics. WebcatPlus now offers links to digitized materials in NDL's Digital Library from Meiji Era. Search CiNii Books, for books held at university and research libraries in Japan. Some books may be borrowed through Interlibrary Loan. (Ask librarian for details). 
E-books in Japan:  Aozora Bunko (青空文庫) is an online e-text collection of out-of-copyright Japanese literary works (fiction and non-fiction including 12500+ titles). Kindai Digital Library (近代デジタルライブラリー) has digitized (scanned from original) copies of public domain items from early-modern to modern Japanese works. Available through Japan's National Diet Library.