The professional vegetable knife: A blade ground to an edge on only one side, with a flat or hollow back; it cuts straighter and finer but takes more skill to sharpen than a double bevel. and significantly harder to maintain than the accessible nakiri.
Signature technique: katsuramuki, peeling a cylindrical vegetable (daikon, cucumber, carrot) into a continuous thin sheet by rotating it against the blade. This is impossible with a double-bevel blade, whose bevels on both sides would cause the edge to wander.
Regional variants: the Kamagata usuba (Kansai) has a pointed tip that allows additional detail work; the squared Kanto usuba is more common outside Japan.
Ideal steel: carbon takes the finest edge here, such as Shirogami #1 or #2, or Aogami #1. The thin geometry and single-bevel sharpening reward a hard, fine-grained edge.
For professional vegetable preparation in a traditional Japanese kitchen; home cooks should use a nakiri.