The H&K MP5K is a compact variant of the MP5. It debuted during Madness Combat 3: Avenger, in which Hank used one against several grunts. It reappeared in Madness Combat 4: Apotheosis with only a slightly modified design. In Vomit, it underwent a complete redesign with a more detailed image. in Madness combat 8,The Auditor spawned two of these to use against Jesus. Near the end of the episode, the Auditor's computer was opened to a website with the following description of the MP5K: "This gun also shoots bullets, surprize, surprize. Booooooooring. I look at this gun and want to barf."
In the updated version of Madness Interactive, it replaces the MP9 as the "CQB" firearm. Jesus uses this weapon against the player in the penultimate stage of the Story Mode. It also appears in Madness: Project Nexus (Classic).
Though the weapon itself does not appear in MADNESS: Project Nexus, the NP-5 can be converted into a form similar to that of the MP5k using Arena Mode's Work stations. It is also possible for it to be found in containers or on enemies in this version.