A noble, a mathematics professor, and the first ever "crime consultant," William is a genius who attempts to overthrow evil nobles and destroy the corrupt class system.

Noriaki Kakyouin is a student who has traveled to Egypt. Dio Brando sensed his Stand powers and asked him for a demonstration, which turned out to be a fight. Afterwards, Kakyouin is brainwashed by Dio using buds from his own cells into following his will, which is to kill Joutarou Kuujou. The manner in which he carries out his assault upon Joutarou differs from the Manga and OVA. In the manga (and the videogame), the assault happens inside a clinic of a school. In the OVA, he attacks Joutarou by possessing the body of a female student with his Stand. Joutarou soon discovers that Kakyouin was under the influence of Dio. Joutarou then used his own Stand, Star Platinum, to successfully remove Dio's implant buds from Kakyouin's head in spite of the risk that it may openly attack both of them, freeing Kakyouin from Dio's slavery. Kakyouin then joins Joutarou's journey to save Holy and defeat Dio in Egypt. Kakyouin's Stand, Hierophant Green, can attack from long ranges and unleash an energy attack known as the Emerald Splash. He maintains a calm demeanor and is often seen with Joutarou, consistently wearing his green school uniform. He's often smiling with an "above-it-all" air, but humbles himself constantly and will go so far as the occasional crude joke to lighten the mood.