Yu-Gi-Oh! GX Manga Only Characters

Ryuga
Mr. Ryuga (龍牙, Ryūga) is a teacher trainee assigned to duel fifty students in Duel Academy. On the condition that he could pass them all, he would be recognized as an official professor of the school. He is rumored to take the cards of those he defeats. When he duels, he uses a special ring to emit an electromagnetic force that disables his opponent's Duel Disk, preventing their use of Spell Cards. He challenges Jaden, but the duelist defeats Ryuga with his Trap "Alternate Fusion" card.

Ryuga uses a Dinosaur Deck, which utilizes the brute force of monsters such as Cyber Dinosaur to defeat his opponents.

Seika Kohinata
Seika Kohinata (小日向星華, Kohinata Seika) is a Obelisk Blue student and Miss Duel Academy for the past two years. However, she discovers that Alexis has the same number of votes. When it's revealed that Jaden has the deciding vote and also happens to be Alexis's friend, Seika suspects that it was a ploy by Alexis in order to win, even though neither Alexis or Jaden has any interest in the competition. Seika challenges Jaden to a duel for his vote, but Alexis decides she'll take Seika's place. If Jaden wins his vote will go to Seika while if Alexis wins, she's allowed to drop out of the competition, making it a win-win situation for Seika. Even though Jaden wins in the end, Seika decides that Alexis should be Miss Duel Academy as she has proved to be better qualified.

Seika later appears to duel Jaden in the finals of the tournament. She uses a Snake Deck.

Koyo Hibiki
Koyo Hibiki (響紅葉, Hibiki Kōyō) is the younger brother of Midori and once a three-time Duel Monsters champion. Koyo was a great Pro League Duelist who used Elemental Heroes. Chazz received an autograph from him, and in the process, Kouyou's "Winged Kuriboh" altered Chazz's "Light and Darkness Dragon" card. However after losing a Shadow Game to a mysterious duelist, he found that every time he drew a card while dueling seriously, the deck of his heart would be depleted, at which point he would die. Kouyou suffered from this and was sent to the hospital where he met a young Jaden who had broken his leg while playing baseball. He taught Jaden all he knew about dueling and to always have fun dueling no matter what. With his health failing, he decided to give up pro-dueling and made Jaden his final opponent. After defeating Jaden, he gave him his deck and his lucky red jacket. However, he found that in this he had drawn the last card, completing the curse and falling into a permanent coma.

Koyo's full name means "autumn colors".

Koyo plays an nature-based Elemental Hero Deck. Before the start of the manga, Koyo gave Jaden his deck, including the one-of-a-kind "Elemental Hero Terra Firma" card.

Midori Hibiki
Midori Hibiki (響みどり, Hibiki Midori) is the headmaster of first-year Slifer Red students at Duel Academy. She is a kind person who actually bought Jaden his first Duel Disk. Though her deck is unknown, she is one of the few duelists that her brother, Kouyou Hibiki, could never beat even when he went pro.

Mysterious Entity
First appearing in Kouyou Hibiki's forgotten memory, this bizarre figure is ultimately responsible for the young duelist's comatose state, dealing him the fatal Penalty Game. Not much is known about this entity, but in Chapter 022 of the GX Manga it reveals that it is actually a Ka (Duel Spirit) captured by the High Priests during the rule of Atem. It's tablet has been shattered, resulting in its need to act through humans by possessing them. It craves other Duel Spirits, as consuming them will allow it to somehow regain its original body. David Rabb and Reggie MacKenzie seem to have some kind of connection to it, the former receiving instructions and even temporary possession through an earring on his right ear.

Interestingly, an image was inserted into the US release of Chapter 13 showing what seems to be a young David Rabb, clearly possessed, challenging Kouyou Hibiki. These images were not found in the original Japanese V-Jump release.

There have been rumors that this entity is Yubel as Yubel has similarly put Osamu, a childhood friend of Jaden's in the GX Anime who bears a suspicious resemblance to Kouyou Hibiki, into a coma. Yubel also desired to regain its shattered body; however, as this entity seems only to take active interest in Jaden upon discovering his possession of the Duel Spirit card, Winged Kuriboh, this is unlikely. A silhouette that may be this person also bears a resemblence to Sartorius. Another suggested theory is that it may be Zorc Necrophades since it is an evil entity which existed during Atem's era, which he had sealed away.

David Rabb
David Rabb (デイビッド・ラブ, Dēbiddo Rabu) is a duelist from the United States and companion of Zane who he follows to Duel Academy. After arriving at Duel Academy along with Zane and Reggie Mackenzie, David participates in the tournament hosted by Duel Academy, easily trouncing Syrus. He later crosses paths with Jaden, but decides not to duel him because of his Slifer Red status as the defeat of a Slifer Red will get him a meager amount of points compared to Ra Yellow and Obelisk Blue students. Because he is fluent in both English and Japanese, he is able to converse with the other characters.

He seems to serve of the mysterious being from Jaden's past and seeks Duel Spirits on its behalf. He is possibly the one who hospitalized Kouyou Hibiki, as, when possessed, his appearance is identical to the black shadow in Kouyou's hazy memory.

David uses a one One Turn Kill Deck, focused around the powers of "The big SATURN".

Reggie MacKenzie
Reggie MacKenzie (レジー・マッケンジー, Rejī Makkenjī) is an American duelist and accompanies David and Zane to Duel Academy. She participates in the on-going tournament hosted by Duel Academy and her first major opponent is Alexis whom she effortlessly defeats. She later questions Alexis about Jaden, seeming to be interested in his ability to see Duel Spirits. Toward the end of the tournament, she is defeated by Bastion, though, oddly, with the cards she had in her hand, she could have easily won. She, like David seems to be acting at the behest of the mysterious person who hospitalized Kouyou.

Reggie plays a Fairy Deck.