Seinen manga are manga whose target audience are adult men - generally aged from eighteen to their mid thirties. This is in contrast to shonen manga; which is for younger men and boys, generally from eight to eighteen years of age.
There is also a female counterpart to seinen manga known as josei, sometimes also referred to as redisu or redikomi; which are manga created to appeal to females in ages ranging from eighteen to thirty.
Of course, these demographics are only averages, and the manga are read widely by individuals outside of their target audiences.
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The rise in seinen manga started when rental magazine systems – also known as rental libraries - began to become popular in the 1950s. These were drawn to appeal to an adult audience and could sometimes contain more mature subject matter. But as these rental libraries' popularity began to decline, the publication of seinen magazines was introduced. It was in 1967 that Futabasha Publishers released Weekly Manga Action. Not long afterwards, in 1968, Shogakukan began the publication of Monthly Big Comic. Because of the decline in the use of the rental system, some of the artists who had previously used it to publish their work began to draw for shonen or seinen magazines.
The introduction of these new magazines created competition in the market between the increasing amount of seinen manga and the pre-existing shonen manga. While shonen manga began to use certain story elements to gain back more readers, seinen manga also fought to retain a majority of subscribers. Ultimately, in 1968 with the release of Shueisha's Shûkan Shonen Janpu, 'Weekly Shonen Jump', and the already existing Weekly Shonen Magazine published by Kodansha and Weekly Shonen Sunday published by Shogakukan, shonen manga began to take back the majority of readers it had in the past.
Seinen manga, as aforementioned, are aimed at older audiences, and the themes presented can often vary. Comparatively to shonen manga, seinen depict more graphic sexuality and violence. As well, instead of teenage main characters, as in shonen manga, the manga often revolve around the life of a college student or businessman. Seinen manga can also be more dramatic than the average shonen manga and may also have political themes.
Again, it is difficult to look at a manga and determine whether it is a seinen, shonen, or even a shojo manga. While the themes can be an indicator, there are two details that can be used to help determine whether or not a manga can be classified as seinen. The first detail is the original magazine that the manga was published in, and whether or not that magazine was a seinen. If the term 'youth', 'young', or 'big' appears in its title, it is most likely a seinen magazine, though this is not a hard and fast rule. The second detail is the inclusion or absence of furigana. This is hiragana (one of the Japanese writing forms) that is written alongside kanji. Since furigana is an aid for those who may not be able to read kanji, its absence can indicate that the manga was intended for an older audience.
Seinen manga is still read today, though it is not as popular as shonen manga. In 1979 Shueisha created Shukan Yangu Janpu, 'Weekly Young Jump', which has become today's leading magazine for seinen manga. Some well-known seinen manga that have been published include series such as 'Golgo 13' by Takao Saito, 'Berserk' by Kentaro Miura, and 'Akira' by Katsuhiro Otomo.
