"Shōnen" and "Seinen" might be terms you have heard of, even if you are new to manga and anime. Along with "Shōjo" and "Josei," they are often used in large anime and manga databases such as MyAnimeList to describe various titles – and there are often conflicting opinions about the correct way to characterize certain works. Here is the full explanation of the terms:
What is Shōnen?
"Shōnen," meaning "boy" in Japanese, is not an anime genre like "fantasy" or "romance." Rather, it describes the marketing practice of targeting Japanese works – initially manga – to male audiences, typically aged 12-18.
Elements of this type of marketing have been around at least since the early 20th century but the post-WWII era was what shaped shōnen manga as we know them, with their fighting sequences, technology, and ofter militaristic settings. Early examples include Dororo and other manga by Osamu Tezuka, while some of the most recent shōnen works include the currently ongoing Jujutsu Kaisen and Kemono Jihen.
While the terms shōnen and shōjo (the female-targeted equivalent) were predominantly used for the manga, due to their serialization in magazines promoted to young boys or girls in their teen years, the terms have come to be used for anime as well. More often than not, they describe anime adaptations of manga marketed as shōnen.
However, as anime became an increasingly popular form of entertainment, certain characteristics came to be associated with shōnen, including a young, male protagonist keen on improving his fighting skills or magic, while most (but not all) shōnen are idealistic; their protagonists will normally see the good in others and achieve victory with minimal casualties.
In any case, it's important to remember that shōnen, while a useful term, is a marketing tool, rather than a genre, and it might appeal to girls as much as to boys. The Promised Neverland, for instance, is shōnen because it was first serialized in a shōnen magazine, even though the main characters are a group of children, with the most important one being a girl. The currently ongoing Jujutsu Kaisen, was also marketed as shōnen even though it's darker than most.
What is Seinen?
The word "seinen" means "youth" in Japanese, but Seinen anime and manga are those targeting young adult male audiences, with the female-targeted equivalent being "Josei."
Once again, "Seinen" manga can be works of fantasy, horror, science fiction, Isekai, or any other subgenre you can think of. The term usually describes the marketing practice and certain characteristics typically associated with a young male demographic (or in some cases older teens or men aged 18-45) without this meaning young adult men are the only ones to enjoy such media.
Some well-known Seinen manga and anime include Berserk, Hellsing, and Tokyo Ghoul.
Of course, since Seinen works often come with specific expectations and sets of characteristics, some classifications are bound to surprise you. Rozen Maiden, for instance, a relatively cute, if a bit dark anime about lavishly-drawn ball-jointed dolls fighting for the favor of their creator, was surprisingly serialized in a Seinen magazine.
While, as we have seen, dark, more cynical shōnen titles aren't unheard of, very dark works, or those with excessive gore and horror elements will most likely be Seinen. Such is the case of Elfen Lied, for instance, though, paradoxically, Death Note was serialized on Shōnen Jump, while Banana Fish an anime about two young men trying to survive abuse, gang violence, and the distribution of a deadly drug was marketed as Shōjo due to the tender relationship between the two.
What Is the Difference Between Shōnen and Seinen Anime
The examples above show us that, the characteristics of Shōnen and Seinen aren't set on stone. The terms are often an over-specification of demographics, that doesn't even describe the actual audience completely accurately, since more and more viewers enjoy the same titles, regardless of gender.
However, there are certain characteristics usually associated with either Shōnen or Seinen, making it easy to classify them mentally, even if their creators categorize them differently. For instance, many Shōnen works tend to belong, often having a "monster of the week" structure and many fillers even when there's an overreaching plot.
Seinen on the other hand tends to be shorter, often with 12 or a maximum of 24 episodes in a single season. In the case of such Seinen works, every episode means something and furthers the plot in unique ways to reach a conclusion that will sometimes be violent or sad, rather than overly idealistic.
Tokyo Ghoul, for instance, has very short seasons, while the slightly longer Monster is very dark, and probably unsuitable for at least the youngest of the target audience of Shōnen. The art style will usually be a bit more gritty and realistic, without the exaggerated facial expressions and funny moments often found in Shōnen.
Just like Shōjo and Josei, Shōnen and Seinen can be useful tools in marketing and anime scholarship, while they can often help viewers find more anime and manga to love based on what their previous favorites are classified as.
Even so, our understanding of gender and genre keeps expanding, meaning that some classifications are bound to fail anime and manga fans. For this reason, it's important to approach (age-appropriate) works with an open mind and not let labels form our opinion about media we haven't yet consumed.