It sure is
The purplish color, lack of dorsal patterning, and large size make it easily distinguishable from all other Japanese salamanders.
"The genus
Pachypalaminus was originally erected for this species on the basis of its having a lacrimal bone in the skull, but it is now known that all
Hynobius have a lacrimal bone, so there is no foundation for classifying it as anything other than
Hynobius."
Source: Guide to the Amphibians and Reptiles of Japan (Goris & Maeda 2004)
They are said in the book to often prey on a large species of earthworm that grows to 16 cm in length.