When you walk, wallet trembling, into that small high-end Japanese eatery with its food preparation area in full view, take a moment to look around for the food processing appliances. It's likely you won't see a single one. All that wonderful fine cutting work on your plate - cabbage, cucumbers, carrots, mushrooms, radish - is accomplished by hand, with an usuba. It is an exceptional cutting tool, a professional's knife not commonly found in the home kitchen in Japan.
The usuba is the first knife a trainee Japanese chef will use and it will be a mainstay knife throughout his or her career. Only after demonstrating competence with the usuba will a young chef move on to employing the other specialist knives available in the workplace - the deba, the sashimi-bocho, the gyuto. Nothing to do with the value of the knives but everything to do with the value of the ingredients. Radishes are cheap and knife skills are honed on them, using an usuba.
Usuba means 'thin blade'. It is designed for efficiently dealing with the industrial-scale chopping tasks in a Japanese restaurant as well as the fine decorative techniques that are a hallmark of Japanese cuisine. People who really know how to get the most out of an usuba get there with hours upon hours upon hours of practise. A really nice knife to have if you wish to use the best tool available for soft vegetables or are serious about taking on Japanese cuisine, but in all truth complete overkill for the low-volume home kitchen.
An usuba will be right-handed or left-handed. Given the delicate single-bevel blade sharpening will always be a concern, so consider that aspect of ownership before purchasing.