The joke of the comic is that Kazuya decided to get rid of the bodies the only way he knows how.
By tossing them off a cliff / into a volcano.
That's the joke.
+ the punchline of the running joke of "Sephiroth is good now"

As for Kazuya in his game series.
He started out as a simple "I wan't to take revenge against my father" character. But then he became a massive evil asshole out to make anyone that opposes him suffer and basically became just like his father.
Also, he has demon DNA in him that let's him become a demon. Metaphorically and and very literally.

Well, I'm not a Tekken Expert but here's what I know: The Mishima Family (the main protagonists of Tekken, and with Heihachi, Kazuya, and Jin, with the former being Kazuya's father and the latter his son) are all kind of assholes.
Kazuya IS the hero and protagonist of Tekken 1 but from Tekken 2 onwards he's a major antagonist. After he (thinks he) kills Heihachi in Tekken 1 he takes control of the Mishima Zaibatsu (their big corporation) and makes it even more corrupt and evil. Kazuya is pretty much the type of guy to laugh at other people's misfortune and be cold and cruel to everyone. With Jun Kazama (Jin's mother) being the one character that he seems to care for and believe there's still good in him.

soo…. yeah, we got another villain in Smash!