Ryo Marufuji or Zane Truesdale (4Kids dub) is a supporting character in Yu-Gi-Oh! GX. Though he at first serves as a supporting character, during the second season he becomes a villain after experiencing a transformation of mind, becoming much more brutal and sadistic, though he later becomes redeemed.
Ryo is pitted against Mad Dog Inukai in the "Underground Duel," a competition in front of a shady audience wherein both contestants are sealed inside a cage and forced to wear electrodes that shock them each time life points are depleted. Ryo finds himself on the losing end again but realizes that his former philosophy of respecting the opponent above the desire to win has limits towards the end of the game. Frustrated and desperate, he resorts to cruelty and aggression and summons the "Chimeratech Overdragon", which wins the duel and practically destroys the dueling ring in the process. As the smoke clears, Monkey Saruyama calls Ryo a monster (he is amazed in the 4Kids dub). The next time Ryo is seen, he proves his strength to the dueling world once more. He is now addressed as "Hell Kaiser Ryo" in the Japanese version. He has donned a dark outfit, and a personality to match. In English Yu-Gi-Oh! video games, this version of Ryo is referred to as "Dark Zane" to differentiate him from his former persona, as both versions are possible opponents.
Ryo returns to the Pro League and goes on a new winning streak and many of his opponents are left seriously injured at the hands of his monsters' direct attacks. In episode 83, Ryo fires his promoter Saruyama and travels into the mountains to confront Samejima in the dojo where he was brought up dueling, hoping to acquire the forbidden Cyber Style Reverse (サイバー流裏, Saibā Ryū Ura) Deck that existed opposite of his own "Cyber Dragon" Deck. Although Samejima manages to keep Zane at bay with his "Cyber Ogre" and various methods of manipulating his opponent's monsters, he is defeated by his own "Cyber Ogre 2" when Ryo betrays his "Cyber End Dragon." Ryo takes his prize but Samejima believes that he will regain the respect he once held for his opponents during the Genex Tournament so gives him a medal that allows him to participate.
Upon returning to Duel Academia to oversee the Genex Tournament, Samejima tells Ryo's old friend, Fubuki Tenjouin, that Ryo is no longer himself and has been controlled by darkness. Fubuki confronts Ryo in a Duel but Zane's new Cyber Style Reverse Deck overwhelms Fubuki, eventually forcing him to give into the darkness and use his Darkness persona. Fubuki believes that he will set the darkness free from Ryo by defeating him but Ryo wins and reveals that he still has complete control over himself and is not being controlled or influenced by darkness like many characters think. He simply changed his personality because he felt like being cruel and ruthless was the only way he could begin winning his duels again.
In episode 95, Ryo approaches Edo Phoenix for a second duel. Sho, however, intervenes and demands to be his opponent instead. Similar to his Duel with Mad Dog Inukai, both players wear electrodes and are subject to the intense physical punishment of a Hell Duel. It becomes clear that, in his current mindset, Ryo spares no one; he is cold, merciless, and sadistic, regardless of whom his opponents are and enjoys witnessing others suffer, even if it is his younger brother he is torturing. Despite Sho's impressive plays, Ryo defeats him when he defuses "Armored Black Dragon - Cyber Dark Dragon" back to its three original fusion components. He then makes his exit, saying that if there is anything he respects at all anymore it is only victory itself. He appears again in episode 102 following a brief run-in with the disguised Rei Saotome, giving her his tournament medal as he is no longer interested in participating and leaves Duel Academy Island. Every single character that met him on the island is shocked by his change, including Edo. Up to this point, Judai was also revealed to have thought that Ryo had just "tried on a new look."
He is not seen again until midway through the third year when he returns to duel Jesse Anderson to supply the energy necessary for the awakening of "Ultimate Gem God - Rainbow Dragon." Later, after hearing about Yubel, he designates it as his final opponent. Soon after, along with Edo Phoenix, he sees Judai and company off on their journey to rescue Johan Andersen in the different dimension, only to get sucked in as well with Edo. By this time, it is believed that prolonged usage of electrodes (later revealed to actually be his Underworld Deck) has left him with fatal heart conditions. In the 4Kids dub, he says that his heart is weak from the electrodes but he never says that his heart condition is fatal (although it is heavily implied).
While in the alternate dimension, along with Edo, he helps Jim Crocodile Cook and Austin O'Brien in their effort to defeat the Supreme King after he possesses Judai. After this task, he decides to restore a traumatized Jaden back to his old self but is unsuccessful as he didn't understand the extent of the trauma that being possessed had done to Judai's psyche. He decides to duel a Yubel-possessed Johan in order to fulfill his dying wish of being immortalized but is defeated and dies from his heart conditions. However, he manages to grant his wish by making his "Cyber End Dragon" an eternal symbol of his skill and strength. Ryo's performance in the Duel and last words along with the wisdom of the others allows Judai to put his problems aside so that he may face Yubel.
Under unexplained circumstances, he returns to Duel Academia after washing up, unconscious, on the beach, with no explanation given to how he survived his heart failing. His heart is still in bad shape but he is put under the care of his brother to recover. It is revealed that his heart condition was caused not by the electrodes but by his Cyberdark Deck. Ryo also appears to have a gentler personality than before as he shows care and appreciation for those around him once again. He later duels Makoto Inotsume, a practitioner of the Psycho-Style, who has made it his goal to destroy all those who use the Cyber-Style. The duel takes its toll on Ryo, as he becomes so weak that he cannot even reach to his own Deck to surrender. Sho attempts to do it for him, then announces that his brother will not surrender but will merely pull out of the duel. Sho then takes his brother's Duel Disk to finish the duel himself but comes to regret his decision as he starts to suffer the same heart problems as Ryo, where the Deck attempts to inflict damage more quickly on Sho due to the cards realizing that Ryo will no longer use them. Sho overcomes this by "making the Deck his own" by combining it with aspects of his own "Vehicroid" Deck. After the Duel with Inotsume, Ryo allows Sho to keep the Deck with him saying he will start over with a new Deck. He also wants to create a new pro league name as a tag team partner with his brother Syrus.