He is voiced by Taiki Matsuno in the Japanese version of the anime, and by Tony Salerno and Marc Thompson in the English version of the anime.
Manjoume is considered Judai's main rival in the same similarity as Seto Kaiba being the main rival to Yugi Muto. He is the younger brother of Chosaku Manjoume and Shoji Manjoume. He and Judai have dueled one another several times throughout the seasons anime. Originally, he used to be a duelist who only respects powerful cards to a duelist who believes any card can be effective. Since being one of the main characters of Yu-Gi-Oh! GX, Manjoume has been fighting alongside his friends against the various threats in Duel Academy. Manjoume, like Judai, also has the ability to see duel spirits, to which he was able to see Ojama Yellow who then becomes his first Spirit Companion and afterwards Ojama Black and Ojama Green after Chazz acquires them. His original deck was Chthonian. His current deck is VWXYZ, Armed Dragons from his stay at North Academy and Ojamas. He used White Knights cards when he was brainwashed into the Society of Light by Takuma Saiou. After returning to Duel Academia, he was demoted to Osiris Red for leaving Duel Academia. He became one of the Key keepers to protect the legendary Three Phantasms cards from Kagemaru and his Seven Stars Assassins.
In the Yu-Gi-Oh! GX manga, he has the same role in the anime series, but later becomes a deuteragonist.
Manjoume can be seen as the Seto Kaiba to Judai. He is shown to be arrogant at first, but throughout the series, undergoes a drastic change for the better. He hated Judai so much that during Judai's tag team duel against the Meikyu brothers to determine whether or not they are expelled, he watched with a malicious smile on his face, waiting for Judai to lose and be expelled. After losing his duel to Judai, he left Duel Academia and ended up in the Arctic Academy, whose entrance exam required the duelist to find 40 cards to make a makeshift deck. From this experience, he learned to appreciate any and all cards, weak or powerful, which have the potential to be useful. After losing to Judai yet again, he returns to Duel Academia but has to be an Osiris Red. After Duel Academia's "takeover," Manjoume had to again make a makeshift deck of useless cards and still won. From then on, his deck had a mixture of powerful and weak cards, even though his deck mostly revolves around weaker cards, namely the Ojama Brothers, Ojama Yellow, Ojama Black, Ojama Green. Chazz always loves the color black when he always wears his jacket everyday due to the dirt doesn't show to his jacket and hates the color white as he claimed he's not like the Society of Light when he called them that includes Asuka and Daichi as geeks and called his Ojama cards to be his "lame monsters" in English dubbed.
When he was brainwashed by Takuma Saiou, Manjoume was ruder and arrogant than before. He defeated the Obelisk Blue students (including Asuka) into the Society of Light and even threw away his Ojama cards after defeating Daichi. But due to the help from Judai and Manjoume's Ojama cards in their duel, He returned back into his old self again.
He is in love with Asuka Tenjouin who does not hold the same feeling for him. Even with her brother Fubuki's help, he was rejected numerous times. He blushed with Asuka wearing Harpie Lady for the Duel Monsters day. After the brainwash from Saiou was undone, Manjoume does not remember that he defeated Asuka and brainwashed her into the Society of Light.