Killer Is Dead is a hack and slash video game developed by Grasshopper Manufacture. It was released for PlayStation 3 and Xbox 360 in August 2013 and for Windows in May 2014. It is published by Kadokawa Games in Japan, Xseed Games in North America and Deep Silver in Europe.

Killer Is Dead is an action game where players take control of protagonist Mondo Zappa. As Zappa, the player goes through twelve story-driven missions selected from a world map; they range from short linear levels to longer levels that require exploration. Some level areas also require the activation of switches to move forward. During missions, Mondo fights a variety of enemies using his katana and cybernetic gun arm; using the latter changes the camera angle to an over-the-shoulder perspective.

The combat of Killer Is Dead relies on maintaining the combo meter. Each time Mondo hits an enemy, he starts a combo chain which grows as long as Mondo lands consecutive hits without an enemy hitting him. At the highest combo level, special attacks are unlocked which provide different upgrade materials. Some enemies can only be finished off with a cinematic final attack, triggered once Mondo has absorbed enough blood from his enemies by chaining together combos. Mondo can both block and dodge attacks. Dodging plays to combat, as dodging at the right moment causes Mondo to enter Adrenaline Rush, where enemies are slowed and Mondo can land rapid attacks. Mondo's gun arm can transform into three gun types; the rapid fire "Bullet Shot" type, the "Freeze Shooter" which fires ice bullets to slow and even stop enemies, and the power "Charge Cannon" which deals higher damage when shots are charged up.

The game features three mission types: story-based missions that move the narrative forward; sub-missions set within the main levels where Mondo must complete tasks that can vary from pure combat missions to retrieval quests; and "Scarlet" missions where the female support character Scarlet issues combat challenges. After completing each mission, the player is awarded with a rank and a consequent level of upgrade items and in-game currency. These can be used for a fourth mission type dubbed "Gigolo Missions". During Gigolo Missions, Mondo goes out with a selection of women and fill up a "Guts" meter by making eye contact, with more intimate areas such as their breasts granting more points. The woman's attachment to Mondo is increased by buying and presenting gifts during the mission; gifts for the women range from flowers and chocolates to types of lingerie. If the women sees you looking at those areas, a second meter decreases and if it empties Mondo fails the mission. Successfully completing Gigolo Missions grants Mondo access to weapon upgrades.

Killer Is Dead is set on a near future version of Earth, where space tourism and cybernetic enhancements have become a reality. A key element of the story is Dark Matter, a malign energy stemming from the dark side of the Moon that negatively affects weak-willed humans and generates mindless monsters called Wires. It is the job of a government-funded group dubbed the Bryan Execution Firm to kill those infected with Dark Matter using people known as "Executioners", although doing so will inevitably lead the chosen Executioner to be overwhelmed by Dark Matter.

The main protagonist is Mondo Zappa, a new Executioner with a business-like attitude towards his work and a liking for beautiful women. His superiors at the Bryan Execution Firm are its cyborg founder Bryan Roses and his second-in-command Vivienne Squall. Mondo is assisted and lives with Mika Takekawa, an air-headed young girl. Three key characters are David, the main antagonist who usurps control of the Moon and directs the Dark Matter; Dolly the Dream Witch, a woman who can enter a person's dreams and alter their memories; and Moon River, the previous ruler of the Moon and one of an ancient line that acted as magistrates and overseers of the Earth. Many characters are thematically connected to celestial bodies; Mondo represents the Earth, David symbolises Mars, Mika the Sun, Moon River the Moon.

The game opens with an unhinged former assassin-turned-kidnapper Tokio being killed by his replacement, his darkness ascending to the Moon. Two years later, Mondo witnesses the death of his predecessor at Bryan's hands. Mondo is then sent on missions against people who have been tainted by Malice, which causes them to become warped into monsters and perform evil deeds. One of his earliest missions is given by Moon River, ruler of the Moon, to kill David after he usurps her. Mondo and David fight, but Mondo is unable to kill him and David cryptically hints that he needs to grow stronger by absorbing the blood of those corrupted by Dark Matter. Moon River decides to wait until the contract can be completed, and Mondo allows her to live with him until then.

Mondo goes on further missions against people infected with Dark Matter. Following each execution, a piece of the targets' Dark Matter and their blood is absorbed by Mondo's arm, causing him great pain. He is also tormented in his dreams by Dolly, seeing flashbacks of Moon River playing with him as a child with a strange blue unicorn; and David attacking his home, killing his mother and cutting off Mondo's arm before being left at the Bryan Execution Firm by the unicorn. During one mission, Vivienne considers killing Mondo as the Dark Matter begins overtaking him. On another mission, Bryan is nearly killed by Mika, who is likewise being influenced by Dolly.