Humor is characterized by an overarching comic, comedic, or humorous plot. Although some comedic device takes up most of the plot—whether it’s a classic trope like mistaken identity or something more complex like a plot that relies heavily on situational irony, the plot can still include romance, fantastical or science fiction elements, tragedy, etc. A book that is categorized as “humor” should make you laugh (or, at least, make a good number of people laugh, since comedy is subjective). Common themes might include situational or dramatic irony; black humor or dark humor surrounding death, disease, or plague; failed romantic attempts; main characters repeatedly making similar mistakes; wordplay; and satire or parody.
If you like this genre but are interested in stories that are largely told through pictures, remember that the graphic novel format can include ANY genre—not just superhero stories and manga. So be sure to check out that collection as well.