Because gothic literature focuses on horror and terror topics. Which later expanded to horror stories like zombies or more terror subjects like mystery thrillers.
Gothic fiction, sometimes called Gothic horror in the 20th century, is a genre of literature and film that covers horror, death and at times romance. It tends to stress emotion and a pleasurable terror that expands the Romantic literature of the time.
Whereas thriller is a genre of fiction, having numerous, often overlapping subgenres. Thrillers are characterized and defined by the moods they elicit, giving viewers heightened feelings of suspense, excitement, surprise, anticipation and anxiety.
the answer is: round.
in literature, round characters are considerably complex and experience or are subjected to unpleasant situations. as a consequence, they go through crucial sentimental and psychological development, which can cause surprise in the readers. in this case, juan's dramatic transformation is related to the adversities he meets at school.