Homosexuality
Banana Fish depicts homosexuality both in the text of the story through representations of male-male rape, and as subtext through the ambiguously homoerotic relationship between Ash and Eiji. Male homosexuality is a recurring motif in manga; while works created in the 1970s by artists associated with the Year 24 Group formalized manga featuring male homosexuality as a distinct subgenre known as, homoerotic themes and subjects had long been a feature of manga. Banana Fish would come to represent a shift for depictions of homosexuality in manga, towards older protagonists and realist writing and artwork, and away from the schoolboy romances and melodramas that had previously defined the genre. Some manga scholars such as Yukari Fujimoto consider Banana Fish as belonging to a continuous artistic canon that includes works by the Year 24 Group, while others such as James Welker argue that Banana Fish is narratively and stylistically closer to the boys' love genre of male-male romance manga that emerged in the 1990s.
Despite Banana Fish's influence and prominence as a manga depicting homosexuality, the central relationship between Ash and Eiji is never rendered as overtly romantic or sexual. Critic Ted Anderson argues that a romantic dimension to Ash and Eiji's bond can be readily inferred from the subtext of the story, writing that "the astute reader understands the unspoken elements of Ash and Eiji's relationship". Manga critic Jason Thompson similarly describes the series as a "love story" expressed "so subtly as to be invisible", noting how "the sensuality in this manga is in Ash teaching Eiji how to shoot a gun, or Ash and Eiji's friendly, teasing, couple-like dialogue." Manga scholar Christina Parte argues that the non-physical nature of Ash and Eiji's relationship mirrors typical manga romances, which commonly focus on a chaste relationship between a man and woman that is never physically consummated; Eiji's sexual and romantic inexperience is similarly typical of a manga protagonist. Thompson considers several potential explanations for the largely subtextual nature of Ash and Eiji's relationship, including Yoshida's stated desire to focus on the emotional connection between the characters, that Yoshida did not wish to risk eroticizing the manga's themes of rape by depicting a romantic or sexual relationship, and the potential influence of manga censorship codes in limiting displays of same-sex romance and sex.
Gender
While the cast of Banana Fish is almost entirely male, several characters – notably Ash and Eiji – are (literally "beautiful boys"), a term for visually androgynous male characters who blend masculine and feminine qualities. Scholars have considered how are regarded as desirable by a female audience not merely for their physical attractiveness, but because they allow this audience to vicariously experience romance, agency, and personal autonomy through a character that is unconstrained by patriarchy. While romance between is tolerated in some contexts in Japan and is thus not necessarily transgressive or subversive on its face, Parte argues that Ash and Eiji's status as allows them to "transgress Japanese gender norms" by resisting gender roles typically associated with female Japanese adolescents.
Per Parte, Ash and Eiji express a degree of gender ambivalence by alternating between masculinized and feminized agency. Ash embodies typically masculine agency in his position as a leader of a street gang, but is frequently feminized through the rape he suffers at the hands of men. Conversely, Eiji possesses the typically feminine trait of nurturing domesticity – he soothes Ash when he is troubled, treats his wounds, and remains at home while Ash fights – but towards the end of the series, it is ultimately Eiji who takes up arms to free an emaciated Ash from Golzine's clutches. Parte argues that despite the American setting of the series, Ash's quest for self-determination ultimately represents a rejection of restrictive Japanese gender roles: both the "good son" (becoming Golzine's heir) and the "obedient wife" (becoming Golzine's sex slave). Thus, through Ash and Eiji's struggles, the ostensibly female reader is able to "escape from Japanese reality" and "resist the pressures of a highly hierarchical gender and sexual system".
Occidentalism
The release of Banana Fish in the late 1980s coincided with a period of fascination with New York City in Japanese popular culture. Schodt notes how the series reflects the Japanese perception of 1980s New York as a "modern Wild West" characterized by rampant crime, drug use, poverty, and racial tension that was "a symbol of everything that was wrong with America", but which at the same time "seemed symbolic of America's raw energy and exciting individual freedoms". Within the New York of the story, Eiji functions as an intermediary for the Japanese reader, echoing earlier manga such as Fire! that used Japanese characters to link works in American settings to their Japanese readership. Parte argues that it is "tempting to see in Eiji the personification of reverse orientalism" as a Japanese character who is captivated by an American, but that his status as a representing a blending of male and female traits allows him to embody a "female internationalist occidentalism" wherein the female reader can vicariously experience an "exotic American setting" that has fewer limits on personal expression.
Beyond its American setting and characters, Banana Fish features frequent allusions to American literature: Blanca's character arc is drawn from Ernest Hemingway's Islands in the Stream, Ash compares his life to Hemingway's The Snows of Kilimanjaro, and the title of the series itself is a reference to J. D. Salinger's short story "A Perfect Day for Bananafish". The "bananafish" of Salinger's story are fish that eat to excess until they are unable to move, and the story ends with the sudden suicide of the protagonist. The symbolic meaning of the bananafish within "A Perfect Day for Bananafish" is the subject of debate, and the significance of manga's title as an allusion to the story is similarly obscure, as there are few direct references to "A Perfect Day for Bananafish" within the manga. Anderson writes that "there are perhaps connections to Golzine's self-destructive greed and Ash’s seemingly suicidal tendencies, but these connections are tenuous at best."
Violence
The action-oriented plot of Banana Fish, characterized by frequent fight scenes, multi-chapter action set pieces, and the extensive use of speed lines, represented a break from the typical visual and narrative conventions of manga. Yoshida has stated that her interest in action stems from childhood, specifically her desire to play active sports like soccer instead of typically feminine pursuits such as rhythmic dance, and that the preponderance of male characters in Banana Fish stemmed in part from her difficulty in imagining stereotypically passive girls in these active scenarios. Violence and its dehumanizing effects recur as a major theme throughout the series, as characters struggle to reconcile their humanity with the violent acts they commit and endure. Ash represents the apex of this theme: a character whose traumatic past has left him resigned to a life of violence, and who faces the conflict between his desire for a "normal" life with Eiji, and his desire to "protect Eiji from the horrors of his violent life".
Sexual violence also recurs throughout the series, with depictions of rape that Parte argues echo scenes of sexual abuse of women in erotic manga. Thompson notes how the series does not contain any explicit depictions of sex or nudity, and how rape is depicted "entirely as trauma and never as titillation", contrasting eroticized depictions of rape in BL manga.
