Ishmelga-Rean resembles a corrupted and hardened Rean Schwarzer in his clothing from Trails of Cold Steel IV. This consist of the outfit being tattered and with the sleeves rolled up, and the introduction of more red elements. In contrast to Rean, Ishmelga-Rean has longer hair, an arm wrapped in bandages and the other red, demonic, with claws and a tattered sash scarf. He also has a black pointed mask covering his eyes that are either pale yellow or glowing red depending on the level of control Ishmelga has.
Ishmelga-Rean varies in personality, at points appearing collected and melancholic, tormented by the suffering he endured and regretful of the friends and family he had to leave behind. On the other hand, he can be be maniacal, attacking to wound indiscriminatly, plotting and calculating to achieve a version of 'world peace' without regard to anyone. In his own words, 'He is Rean, but Rean is not him'. After Ishmelga is purged from Ishmelga-Rean, this Rean still believes in sacrificing himself for the greater good.
Ishmelga-Rean was a calculated existence brought into being by the near limitless predictive ability of Elysium, which had enough processing power to be able to 'predict futures'. Ishmelga-Rean is the result of one such prediction, following a course of events where Rean did not achieve the blessing and Earth Cage from the spirit of Argres and flew out the atmosphere after winning the final Rivalry at the end of the Great Twilight. In other words, this version of Rean is from the normal ending of Trails of Cold Steel IV where he sacrificed himself. During these events, Ishmelga's thoughtform and Rean fought for control, eventually twisting and merging with each other until a new personality emerged - a personality with control over the perfect completed form of the seven Divine Knights, Zoa Gilstein.
This new "Zeroth Divine Knight" possess all the powers of the original seven and more such as instantaneous long range teleportation, the ability to attack spiritual forms, the ability to call forth lightning, and levitation. The ability to generate spiritual weapons, akin to Testa-Rossa was displayed, as was a 'boost form' similar to that of Ordine, albeit red.
This new personality that was created was enough to hijack Elysium and expel the current system administrator, Lapis Rosenberg. He is set about achieving human progression and peaceful world at any cost, utilising the vast computational powers of Elysium's system. Technology to recreate artefacts such as the Sonorous Seashell and the Monarch's Regalia's abilities was used to disrupt communications, Gnome masks were used to take control of Ilya Platiere who could perform a dance that replicated the effects of the Great Twilight, enthralling others, communication was made with key figures such as Cao Lee, Dieter Crois, F. Novartis and more, and Simulacrum of more powerful figures were created to fulfil other roles, namely Rufus Albarea, the figurehead for his plan: Project: Babel. Manufacturing plants were used to smuggle vast amounts of resources to a secretly constructed facility: Reverse Babel and the construction of an extremely powerful weapon, the Keraunos that would subjugate the various powers of the world. Vast quantities of powerful archaisms and Zauber Soldats were created as well.
Ishmelga-Rean first appears piloting his Divine Knight, Zoa Gilstein in the Nord Highlands, disabling both the Courageous II and the Merkabah Number 8. His primary objective was to remove two obstacles from his plan as well as begin a process where Rean Schwarzer synchronized with the simulated existence. Rean finds himself inadvertently having memories of the timeline that never happened and uttering phrases by the other Rean.
This version of Rean is first seen in person in the Castle of Mirrors, where Rean duels him in a one-on-one fight, breaking the mask that he thinks is controlling him. This turns out to be a ruse, as the Rean underneath suddenly becomes much more aggressive and summons Zoa Gilstein, who had until now been taking the form of Zoa Balor. He withdraws from the Castle in the Zeroth Divine Knight. Following the destruction of the Rufus simulacrum and liberation of Crossbell, Ishmelga-Rean reveals Reverse Babel and destroys Juno Naval Fortress with it.
The calculations and defences of Reverse Babel are enough to repel all attacks. However, the tides suddenly turn when the Arseille II appears, forcing Elysium through a series of unpredictable loops that is eventually exploited. This prompts Ishmelga-Rean to personally intervene, although he is only able to separate the group into two halves and teleports back into the control room, waiting for their arrival. Ishmelga-Rean explains his existence to the party and what he is doing is justified, although the party is unconvinced and attacks him. He easily overpowers them with Zoa Gilstein until the Divine Knights return. Overconfident with the power of all seven Knights at his disposal, he is defeated by attempts a last-ditch effort to assimilate Rean.
Rean manages to have a discussion with his other self before ending him with a final cut, refusing to handle the burden alone. This separates Ishmelga from Rean, allowing Ishmelga to take over and continue fighting until Elysium is shut down and he can no longer exist. In a dying throw, Ishmelga turns over Keraunos' control to the consciousness of humanity and it begins to target places loathed by the people. In a desperate attempt to rescue Rufus before he sacrifices himself, Lapis Rosenberg, Lloyd Bannings, Zeit and Jusis Albarea make an attempt to get into Reverse Babel where they meet Rean who is free from Ishmelga. Rean feels happy at the fact that he is able to meet Jusis and Lloyd again, and offers them knowledge of the future to overcome in three years, but Lloyd declines, saying that they will be able to face any problem that the future brings.
- The scarf Ishmelga-Rean wears is extremely reminiscent of the sash worn by Giliath Osborne, possibly taken from his dead body in the alternate timeline.