You can use the “Use Search Option Only (検索機能のみを利用する)” by logging in as a guest under “Users without Registered User ID (登録利用者IDが無い方)”. Simple search by keyword can also be done from the 簡易検索 (Simple Search) option.

CiNii is a Scholarly and Academic Information Navigator for searching books and journals held by university libraries in Japan.

This database is from National Institute of Japanese Literature to search early Japanese Books.

Use the UIUC catalog to find books, periodicals, etc held by the University of Illinois. You can filter by language to get Japanese search results

Use the I-Share catalog to find books not available at the University of Illinois (either because another patron has already charged this book, or because the book isn't part of the collection here). I-Share is a single catalog through which you can search and request books from the collections of 85+ academic and research libraries in Illinois. You request books from a participating I-Share library the same way you request books from University of Illinois libraries—simply click the "Request Item" tab, log in to your account (the same account you use to manage books you have borrowed from the University of Illinois Library), and complete the request.

Searching WorldCat can often provide better search results when using Kanji or Romaji. In addition, WorldCat provides holdings information and ILL links to libraries around the world. In recent years, Waseda University and Keio University in Japan have begun to include records in this database as well.

Hathi Trust is a partnership of academic universities and research institutions. Full text versions of digitized books and journals are available on Hathi Trust.
Keio University is part of Hathi Trust and has numerous resources in Japanese