Sashimi Knife is a long knife used by sushi chefs. It is correctly termed as the sashimi knife and not a sushi knife.
The blade of the sashimi hocho (sachimi bocho) is long, and thin in order to be able to slice fish in one stroke. They are sharpened daily and immersed in water for one night to get rid of metallic smell that can transfer to thesashimi.
When slicing fish, the knife should be dry, but when cutting sushi rolls it must be dipped in water to make it easier to cut through the sticky rice. It is important to keep the sashimi knife free of smell. They are wiped every single time they the scent from prior ingredients are cleaned. They should never be used to cut condiments.