From a traditional publishing standpoint in the Japanese manga industry, seinen describes anything targeted toward young men over 18. Nowadays, much broader audiences enjoy seinen manga, mostly because it delves into more adult themes. Seinen manga may concentrate on war, fighting, politics, sci-fi, fantasy, history, love, sports, or humor. Like any other genre, seinen encompasses an extensive variety of artistic styles and themes.
Source：https://www.cbr.com/best-current-seinen-manga-ranked/
