The Katana is a Bonus Weapon in Resident Evil: Revelations 2.
The Katana is made available for purchase in the Rewards menu by clearing all of the episodes in Invisible Mode for 50000 BP under the name "Bonus Weapon: Lil' Something Special Just for Moira". It is equipped by going to a workbench via a toggle option, it does not use any slots. Once equipped, it replaces Moira's crowbar. Like all Bonus Weapons, the player will only get a C rank for the chapter if used.
When using the Katana, Moira steps forward as she swings and up to three attacks in a row can be used in quick succession. It is very powerful and can kill most enemies in one strike.
The Katana also appears in Raid Mode as the "Samurai Sword" skill. Unrelated to gameplay, Moira's Urban Ninja costume has a katana sheathed on her back.