Mogizo has long wavy light hair that covers his face. During his flashback, he wears a light-colored traditional Japanese-style robe. His irises are light with cracked markings below his lower eyelids. Despite his age, he retains a youthful and strong physique, due to his vampirism. Like other vampires, he also bares fangs and sharp nails. He always wears a thick layer of greasepaint makeup to hide his youthful appearance, making himself appear older.
Mogizo is a reclusive man who hates all humans, believing that they are shallow creatures with evil hearts. As a vampire, he always locks himself in a separate room claiming he has an allergy to ultraviolet rays, not allowing anyone to approach him during the day. However, he joins his family for dinner and would go out at night. Despite it seeming as if he didn't eat anything else, he didn't suffer from malnutrition, implying that he would drink blood.
Mogizo claims that he has personally witnessed how depraved humans are. Although others thought he went insane because of World War II, he mentions the war was just a game to him since he became a vampire before that. He is inspired by Kars, who believed that the people who succeed are those who solely focus on winning rather than things like pride or conviction. Thus, like Kars, he is a megalomaniac who desires to stand at the top of the world. Believing that his grandson is not so different from him, he chooses to pass on what he learned from Kars.
Although he hates humans, Mogizo puts on an act when talking to others, having a pleasant demeanor. As a result of his strange habits, the people in his neighborhood call him a hermit.
At some point, Mogizo had a son with an unknown woman and he was in the military. Before World War II, he was deployed to St. Moritz, Switzerland on an intelligence operation. There, he witnessed something that transcended all of creation. It is implied that Kars turned him into a vampire, but it is unknown how he escaped. Since he got married and had a child before becoming a vampire, he never told his family the truth about himself or what he learned back then.
Decades later, he speaks with his grandson, Kazuki Karaiya, in Japan and advises him to never open his heart to other humans. He feels that Kars's ideology lives on in him and passes on those teachings to Kazuki. He plans to give a part of his vampiric essence to Kazuki when he becomes an adult so that they could stand at the top of the world together. However, Mogizo suddenly disappears when Kazuki is in elementary school. There were mysterious foreigners in his neighborhood back then who disappeared at the same time, implying Joseph Joestar and/or the Speedwagon Foundation killed him. People in Mogizo's neighborhood speculated that some incident might have occurred, but they forgot about it over time.