Noah is the "Nameless God" summoned by Isamu Nitta using the Magutsuhi he gathered from the Amala Temple in order for it to become the demonic sponsor for his Reason. Isamu mentions that it had been so far removed from the time stream that no one remembers its name, a feat which represents absolute solitude. Isamu grants it the name of "Noah" and then encases himself in a red shell and hibernates inside Noah's head.
Noah will be fought in all paths except in the Musubi-aligned path, where he is slain by Baal Avatar. Defeating him will grant the key item Netherstone. Noah's location does not directly block the passage to the next section of the tower, so it is possible to ignore him and head straight to the shop after him to buy the Kailash Magatama in order to learn "Freikugel" which is especially helpful in this fight when empowered by "Pierce". However, the player still requires his Netherstone in order to gain access to Kagutsuchi, this just allows the meeting with him (whether it will result in a fight or not) to be pushed a bit later before facing Kagutsuchi.
Should it fight with the Demi-fiend, it eventually begins to break down, and its shapeless head transforms into an image of Isamu's face. Noah commences the fight with no natural elemental affinities; however, once it has cast its signature move, Aurora, it will gain Reflect Phys and will reflect three of the four magical elements at a time. Also, at this stage Noah will gain a 90% resistance to Almighty.
Noah has the ability to alter its elemental vulnerability with each casting of Aurora. To reveal the element he is vulnerable to at any point in the fight, the player must observe the type of attack Noah casts - if it casts an Agi spell, it won't reflect Bufu spells, and viceversa. If it casts a Zan spell, it won't reflect Zio spells, and viceversa. He follows a consistent pattern through the fight.