 The root of this genre is in part the contemporary belief that same-sex love was a transitory and normal part of female development leading into heterosexuality and motherhood.Class S stories in particular tell of strong emotional bonds between schoolgirls, a mutual crush between an upperclassman and an underclassman.Around the 1970s, "yuri" began to appear in "shōjo" manga, presenting some of the characteristics found in the lesbian literature of the early twentieth century.