XIII is a first-person shooter with elements of stealth and action in certain missions.[3] The game centers on the main character, named XIII, who has awakened with amnesia. He uses a variety of weapons and gadgets to uncover the mystery of his identity throughout the 13 chapters and 34 missions. The characters and weaponry in XIII are cel-shaded, giving a deliberately comic book style appearance, including onomatopoeic words contained in bubbles for sound effects. It uses Unreal Engine 2[4] because it was "really strong for level design" and allowed development "across all platforms using one engine".[5] The graphics were compared with Jet Set Radio Future and Auto Modellista.[6] The developer felt that the appearance reflected the comic book and innovated in its portrayal of violence; blood splatters are shown in a cartoon manner.[7]
XIII includes 16 weapons, from a knife to a bazooka, an Uzi to an M60. Objects such as bottles, chairs, or brooms may be used as weapons.[5] Kevlar gear, helmets and first aid boxes are scattered throughout the map. People can be taken as hostages or as human shields, preventing enemies from firing on the protagonist. Lock picks are used to unlock doors and grapnels to climb on walls. Through the "sixth sense", XIII can hear enemies behind walls with the aid of "tap-tap-tap" signals. Stealth operations include strangling enemies or hiding dead bodies.[7] Comic strip-style insets pop up at the top when a headshot is performed or serve as clues or tips for the player.