This item is also featured in Cross Edge as Ayatane's exclusive ultimate weapon, although it was renamed to "Shadow and Eternity" in there. Like all the other ultimate items, it's very hard to synthesize, and the unique ingredient required to synthesize it is also pulled directly from Ar tonelico: Melody of Elemia: it's Kant's Firebox, although it was renamed to "Kant's Firebox?" in there.