Detail from Ashita no Joe (Tomorrow's Joe) by Tetsuya Chiba.
In weathering the struggle of rebuilding their country since the war, and now of reviving the economy since the recession, the Japanese have continued to find inspiration and solace in shonen manga heroes. It's somehow fitting that the word shonen not only means "boy"...but also "pure of heart."
— Paul Gravett, Manga: Sixty Years of Japanese Comics
In the late 50s, the dynamic expansion of Japan’s economy fueled a period of intense growth in the manga industry. As the children of the postwar baby boom reached manga-reading age, publishers realized their voracious appetite for new stories could support weekly titles, rather than the monthly offerings that were the current standard. On March 17th, 1959, competing publishers Kondansha and Shokugan launched the first weekly manga anthology magazines for boys: Shonen Magazine and Shonen Sunday, respectively.
Of course, much of the manga of the postwar period had been aimed at this adolescent male demographic and was similar in content; however, the advent of the weeklies ushered in a period of explosive creative output, forcing studios to literally quadruple their workload and launching the careers of a new generation of mangaka. The adoption of faster production processes prompted a shift to working primarily in black and white, which is still the standard today (Rousmaniere, 2019, p. 25).
Shonen was (and remains) the best-selling genre of Japanese comics, and it shared “most of the action and comedy themes common to post-war boys’ comics worldwide” (Gravett, 2004, p. 56). Sports titles like Tetsuya Chiba’s Ashita no Joe (Tomorrow’s Joe) and Ore wa Teppei (I’m Teppei) competed with samurai stories like Osamu Tezuka’s Dororo and martial arts epics like Buronson's Fist of the North Star. An early innovation in the shonen category was “mecha,” which dealt with giant fighting robots controlled by human pilots. Mitsuteru Yokoyama’s 1956 title Tetsujin 28 was an early preview of this subgenre, but it truly caught on with Go Nagai’s Mazinger Z in 1972.
Detail from Ghost in the Shell by Shirow Masamune.
By the late 1960s, the baby-boomers—whose appetite for manga had sustained the shonen explosion of the late 50s—were entering their early 20s. Seeking to stay relevant to the developing tastes of this massive readership (known as the dankai or "clump" in Japan), manga publishers began bringing out magazines that dealt with more mature themes and adult subject matter, traditionally the purview of alternative manga and gekiga (Hideaki, 2013). Early seinen ("youth" or "adolescence") forerunners like Young Magazine, Big Comic and Manga Action were followed by a wave of imitators over the following decade, their circulation buoyed by the economic bubble of the 1980s (Gravett, 2004).
Early seinen focused heavily on traditional "men's interests" themes of action, violence and sex. Popular titles followed characters that fulfilled male power fantasies: browbeaten salarymen packed on subways could lose themselves in the exploits of the womanizing globe-trotting super-thief Lupin III, the ruthless and ultra-violent hitman Golgo 13, or the masterless wandering samurai Lone Wolf.
However, seinen has always been an amorphous category encompassing a wide array of stories and content, especially in the current day. My Brother's Husband by Gengoroh Tagame is the heartwarming story of a somewhat-prejudiced Japanese man getting to know his estranged, deceased brother's widower. Taiyō Matsumoto's fantastical Cats of the Louvre follows a group of cats living in the titular art museum, while Hana-Chan and the Shape of the World is a gentle tale about an imaginative girl exploring her home town.