The katana is unusable by the player and only seen being wielded by some Japanese soldiers during certain parts of the campaign mode. In the first mission, "Semper Fi", a Japanese soldier playing dead stabs Rooker with a katana. Another slashes Miller across the shoulder with a katana as he tries to escape with the other Marines. Also, in the last part of "Little Resistance", Sgt. Tom Sullivan gets killed by a Japanese Banzai Charger wielding a katana. Katanas are usually replaced with the Bayonet by the Japanese soldiers, however they can be seen on some of the soldiers' uniforms even if they are not used.
Examination of the game files reveals the menu and pickup icons for the katana, hinting it was originally going to appear as a usable weapon at some stage of development, at least until it got scrapped.
The Katana appears in the Multiplayer of Black Ops III, though it is only seen being used by the Specialist Spectre as part of his Epic Taunt, which can only be unlocked from the Black Market. An actual usable Katana, the Path of Sorrows, was later added in the Black Market for Multiplayer, and is a secret unlockable weapon in Revelations.