The Japan P.E.N. Club Digital Library

Most of them (if not all of them) are in the public domain.

http://www.japanpen.or.jp/e-bungeikan/

Novels:

http://www.japanpen.or.jp/e-bungeikan/no...bhome.html

Translations (of European works):

http://www.japanpen.or.jp/e-bungeikan/tr...nsltn.html

Tanka and Haiku:

http://www.japanpen.or.jp/e-bungeikan/ch...bhome.html

Anti-War:

http://www.japanpen.or.jp/e-bungeikan/an...bhome.html