They can be extra ordinarily sexually graphic or violent, and usually both, because manga isn’t regulated like other forms of entertainment are in Japan, thus there are virtually no limits on what is printed.
Anyway, I’ll bet that comic cured the kid of any desire to be a weeaboo. He should stick with Spiderman.
Manga is basically comics. Hentai is the violent and graphic type. Sailor Moon in comic form would be general manga. However, Sailor Moon doing the deed would be hentai.