Killer is Dead is an action game that features violent action, a main character wielding a katana as the most prominent weapon, assassins as an important theme, and a cel shaded visual style. The game is divided into 12 episodes in locations all over the world and stars Mondo Zappa as the main character. He is a contract executioner who works for the Bryan Execution Firm. The game is set in the future and Mondo receives jobs to kill cyborgs and assassins. Before each mission, a brief overview of the objective is shown against a world map, and in between the fighting, there are often animated sequences that further the story. Completing a main mission usually opens up several side missions. The main character wields a katana called Gekkou with his right hand for attacks and to deflect bullets. It absorbs blood, filling up a meter, enhancing Mondo's fighting ability. Combos increase the attack speed, and a moon slash can be performed as a powerful attack. His left arm has a cybernetic enhancement, Musselback, which is used for various operations, including solving puzzles and discovering hidden areas. Mondo can turn it into a regular human hand to crack fingerprint codes or change it into a ranged sub weapon that shoots projectiles. Separate buttons are used to block and dodge. Defeated enemies leave behind body parts that recover health and blood.
After each mission, Mondo receives a payment based on his performance, which is based on statistics such as completion score, total damage bonus, rescue payment, and toughness payment. Upgrades through moon crystals are divided into three categories: attack skills, sub weapon skills, and special skills, unlocked gradually and with a fixed progression for each type. In the main office, different types of costumes for various characters can be equipped, and there is a gift shop where cash can be spent on various items.
There is also a mini-game where Mondo gets to seduce women by taking pictures with Gigolo glasses. By timing when they are looking away and targeting specific areas, sexy pictures can be taken to provide moans of ecstasy and briefly remove certain clothes, revealing their desires. Timing is important to fill a guts gauge, because otherwise Mondo becomes nervous.
The retail US edition was provided at launch with additional content, including an art book and a soundtrack disc. The PC release called Killer is Dead: Nightmare Edition also includes the Smooth Operator DLC as well as a new Nightmare difficulty mode and a theater mode to re-watch cut-scenes.
