The main characters in yaoi usually conform to the formula of the seme (the "top", or dominant figure) who pursues the uke (the "bottom", or passive figure).
Material classified as yaoi typically depicts gay relationships between male characters and may include homoerotic content.
The word was originally used to describe an author's distinctive style, for example, the styles of Yukio Mishima and Jun'ichirō Tanizaki.
Akiko Mizoguchi describes its application to male-male stories as "misleading", but notes "it was the most commonly used term in the early 1990s." and were replete with "philosophical and abstract musings".
Although the yaoi genre is also called Boys' Love (commonly abbreviated as BL), the characters may be of any age above puberty, including adults.
Works featuring prepubescent boys are labelled shotacon and seen as a distinct genre.
Characteristics of shōnen-ai include exoticism, often taking place in Europe, Jeffrey Angles particularly notes Moto Hagio's The Heart of Thomas (1974) and Keiko Takemiya's Kaze to Ki no Uta (1976–1984) as being groundbreaking, noting their portrayal of intense friendship between males, including jealousy and desire.
The tachi partner is conceptualized as the member of the relationship who pursues the more passive partner, the latter of whom is referred to as the neko.
Seme and uke is similar but not identical to tachi and neko because the former refers primarily to sexual roles, whereas the latter describes personality.
Aleardo Zanghellini suggests that the martial arts terms have special significance to a Japanese audience, as an archetype of the gay male relationship in Japan includes same-sex love between samurai and their companions.
Another way the seme and uke characters are shown is through who is dominant in the relationship - a character can take the uke role even if he is not presented as feminine, simply by being juxtaposed against and pursued by a more dominant, more masculine, character.