According to the game's Steam page, the PC version of Killer is Dead will be available on May 23rd. This new PC version, that will be titled Killer is Dead: Nightmare Edition contains the following add-ons:
A new Nightmare Mode difficulty, where enemies can only be defeated using the Adrenaline Burst, Dodge Burst and Headshots. Final Judgement QTE finishers will be unavailable to the player in this mode as well.
Theater Mode, that lets you rewatch cutscenes and acquire extended background info on all of the game's characters.
Smooth Operator DLC, pack that includes X-Ray glasses, costumes and new mission.
To know more about the title, check out our review of the original version of Killer is Dead.