Isaac is a tall man with an unusually long ahoge. In the past, he didn't wear much armor and he had more relaxed features. He was usually smiling and had big eyes. In Dunya's creation, he wears armor and usually seems to have a bored look.
Isaac cared for Dunya very much and even sacrificed his life in order to save the princess. Even in death all he wished was for Dunya to be happy.
Isaac was Dunya's servant in Musta'sim Kingdom. She was raised by Isaac's mother, so the two grew up together and were very close. One day, Isaac performed a knighting ceremony, swearing he will always be by her side to protect her. They often played together as children, remained close, even as they grew older. When Dunya was thirteen, she was engaged to an archduke of a Musta'sim's neighboring country. She returned Isaac's sword and commanded him to serve, not just her, but the entire Musta'sim Kingdom. He agreed to it, though he was crying, so Dunya reassured him that he was a good person. Soon after, the two of them bid each other farewell.
At the war of the scholars and the nobles, Isaac tried to escape the kingdom in order to save Dunya. After the nobles were killed, the scholars and palace guards wanted the Royal Family's heads to be presented to the crowd. Isaac tried to explain the situation, that the princess wasn't aware of the situation and had not sinned, but he was killed anyways. Dunya witnessed this, as well as the guards saying it was all according to "fate".
Isaac arrives, together with Dunya and Ithnan, in the Torran Village where the Dungeon Zagan is located. They present themselves as merchants from the Reim Empire and ask the people for baptism. They say that their goal is to buy Torran crafts.
While the Fake Zagan is telling Aladdin, Alibaba Saluja, Hakuryuu Ren and Morgiana about the real Zagan in the treasury room, Dunya attacks the little creature causing it to die instantly. When Alibaba realizes that they're merchants they met earlier, Isaac takes off his sword but is stopped by Dunya, who asks with a smile if she commanded him to do anything. He humbly apologizes and justifies himself that that insolent fellow addressed to her as a "merchant" again, but Dunya tells him to not be so angry. Dunya then attacks them.
After Dunya's attack towards the group, the Musta'sim Princess introduces herself and her knight, Isaac. After some talk occurs, Dunya commands Isaac and Ithnan to not interfere because she wants to prove her worth by herself. She changes into Black Djinn and attacks Aladdin. Alibaba tries to help him, but Isaac stops him. First, he easily overpowers Alibaba. He yawns and notes that he's too slow. He says that Alibaba can only swing his huge clumsy sword inefficiently. He wonders why the Magi chose him instead of Dunya. He confesses that he can't stand both him and Magi, and attacks Alibaba again. However, when Alibaba changes the huge Amon's sword to the Amon's Royal Sword, Isaac notices that his battle stance and swordplay completely changed. He hurts Alibaba in the forehead and says that it's not enough, but then realizes that Alibaba's attacks aren't half bad. After that, Alibaba cuts off his arms and legs.
Although being chopped plenty of times, when Dunya orders him to stand up and fight, Isaac's parts of body come together and he fulfills his Queen's order. He activates his Household Vessel, Al-Qaus Kauza, that allows him to move to an incredible speed due to magnetism. He is able to easily overpower Alibaba again. One of his attacks are stopped by Aladdin's Borg. Then, Ithnan gives Lightning Magic to Isaac and Dunya. While Dunya summons her Extreme Magic, Rea Bard, Isaac blocks Alibaba and Hakuryuu's attacks, not allowing them to interfere. He wants to kill Alibaba, but Hakuryuu stops his attack by letting him pierce his arm. In this moment, Aladdin uses Shallal Raqi on him. Alibaba slashes him, dismembering his entire body. After Dunya's magic fails he tries to protect her, but after Alibaba's slash, he can't fully regenerate, since she ran out of Magoi and her Lightning Magic was the only thing that maintained his body, he falls apart and becomes only sand.
Dunya collapses and starts to cry, so Aladdin uses Wisdom of Solomon to find Isaac's Rukh and they meet for one last time. Isaac's final words are: "Please find happiness" and he embraces the princess. He then vanishes.
He is shown to be skilled in swordplay possessing similar level of skill to that of Sharrkan. When combined with his Dark Household Vessel his swordplay becomes unpredictable.
Dark Household Vessel
- Al-Qaus Kauza (Black Magnet Armor): It gains it's power from the Dark Djinn, Dunya Musta'sim. Al-Qaus Kauza repels the strong magnetic forces between the Earth's surface and it's armor. This results in superhuman acceleration.
Isaac cares deeply for Dunya, even as a puppet he obeyed all of Dunya's commands. Though he was not happy with the news of Dunya being married to a duke, he accepted it for Dunya's sake. With his last words, he embraced the princess and fades with a smile.
- Isaac (יִצְחָק) is a Hebrew name, meaning He Who Laughs.
- Isaac of Mosul is a tale in One Thousand and One Nights.
- Due to his hairstyle, Isaac bears a resemblance to Sōsuke Aizen, the main antagonist of the manga, Bleach.