I think I may actually have to make Dietrich's fire breath a Noble Phantasm, considering its power. In the legend, when he dueled Siegfried, he almost lost due to Siegfried's hardened skin, but Dietrich was enranged after being falsely told that one of his closest friends died, and unleashed his breath on Siegfried, defeating and almost killing him.


That being said, I figured it could be a rather devastating NP in that it can pierce through most defenses, seeing as he almost killed even Siegfried with it. To balance him from using it whenever possible, I'd say it's only limited to when he's enraged.