Japanese manga is published in magazines that target specific demographic categories: shōnen (boys), seinen (adult men), shōjo (girls), and josei (adult women). These are publisher-side marketing categories, not genres. A 'shōnen' work may be a romance, a historical drama, or a fantasy; what it shares with other shōnen works is its target readership, not its content register.
The four categories
- Shōnen (少年) — boys, roughly ages 8–18. The largest segment by circulation. Flagship magazines: Weekly Shōnen Jump (Shueisha), Weekly Shōnen Magazine (Kodansha), Weekly Shōnen Sunday (Shogakukan).
- Seinen (青年) — adult men, roughly ages 18 and up. Flagship magazines: Big Comic Spirits (Shogakukan), Young Magazine (Kodansha), Morning (Kodansha), Afternoon (Kodansha), Young Animal (Hakusensha).
- Shōjo (少女) — girls, roughly ages 8–18. Flagship magazines: Nakayoshi (Kodansha), Ribon (Shueisha), Ciao (Shogakukan).
- Josei (女性) — adult women. Smaller and more diverse than the other categories. Flagship magazines: Feel Young (Shodensha), Cocohana (Shueisha), Be Love (Kodansha).
Why the categories are not genres
A common misconception in English-language fandom is to treat 'shōnen' and 'seinen' as content categories — fast-paced action vs. mature drama. This is approximately true on average but wrong in the particular. Yotsuba&! is a seinen manga but is a quiet domestic comedy; Demon Slayer is shōnen but contains substantial body horror. The categories are stable predictors of magazine, not of plot, register, or tone.
How a work gets categorised
A work's category is determined by the magazine that publishes it. The same author can produce work in different categories by serialising in different magazines: Rumiko Takahashi has shōnen series (Inuyasha, in Weekly Shōnen Sunday) and seinen series (Maison Ikkoku, in Big Comic Spirits) in her catalogue.