In general same-sex relations in premodern Japan were not morally proscribed, though it was rare for an individual to self-identify as being exclusively dedicated to same-sex relationships. Instead, the most common articulation of same-sex relations in extant historical evidence is found in the common phenomenon of men, particularly powerful men, having regular sexual relationships with both women and men, usually younger men. Thus it is perhaps more accurate to say that male-male sexual relations in particular were widely accepted in premodern Japan and represented in primary sources. One good study is Gregory Pflugfelder's book Cartographies of Desire: Male-Male Sexuality in Japanese Discourse, 1600-1950.

We also have a number of excellent books on the history/literature of women in premodern Japan that include some attention to sex, including Janet Goodwin's Selling Songs and Smiles: The Sex Trade in Heian and Kamakura Japan and Marcia Yonemoto's The Problem of Women in Early Modern Japan to name just two. Neither mentions same-sex relations among women, unfortunately, presumably because of an absence of evidence in the primary sources.

The historian Gary Leupp wrote an article titled "'The Floating World is Wide': Some Suggested Approaches to Researching Female Homosexuality in Tokugawa Japan (1603-1868)," Thamyris 5:1 (Spring, 1998): 1-40. His work has been criticized for applying contemporaneous, Western terms such as "homosexuality" in anachronistic ways, but having said that, this article is one of the few attempts by a scholar to address this topic in English.

Some of the most lively representations of same-sex relations in premodern Japan can be found in the fiction of Ihara Saikaku, which has been widely translated into English. The following stories/books in particular are useful: The Life of an Amorous Man; The Great Mirror of Beauties: Son of an Amorous Man; Five Women Who Loved Love; The Life of an Amorous Woman; and The Great Mirror of Male Love. Remember, of course, that these are artistic works that often parody social and cultural realities rather than accurately representing them.