John Romero's Daikatana, better known as simply Daikatana, is a 2000 first-person shooter action role-playing game developed by Ion Storm and published by Eidos Interactive for Windows. A port to the Nintendo 64 was released the same year by Kemco. Players control a swordsmaster who travels through various time periods using the eponymous Daikatana, a powerful sword tied to the fate of the world.

Daikatana was directed by Ion Storm co-founder John Romero, a co-developer of the influential first-person shooters Wolfenstein 3D (1992), Doom (1993), and Quake (1996). Announced in 1997 as Romero's first game after leaving id Software, it underwent a troubled development that saw a change in its engine, release date delays, and the departure of several staff members. The protracted development, combined with promotion that focused on Romero's involvement over the game itself, resulted in negative publicity for Daikatana prior to its release.

Released in May 2000, Daikatana received generally negative reviews for its outdated graphics, gameplay, repetitive sound effects, and poor artificial intelligence. It also sold only 40,351 copies, becoming one of the biggest major commercial failures of the video game industry. Due to the negative response, a separate version for the Game Boy Color did not receive a North American release; it was released in Europe and Japan to a more positive reception.

Daikatana is composed of 24 levels (18 in the console version) divided into four episodes, with a varying number of levels per episode. Each episode represents a different location and time period: Japan in 2455 AD, ancient Greece in 1200 BC, the Dark Ages in Norway in 560 AD, and near-future San Francisco in 2030 AD.

One element that Daikatana stressed was the important role of Hiro Miyamoto's two sidekicks, Mikiko Ebihara and Superfly Johnson. The death of either sidekick resulted in failing the level, and their assistance was required to complete certain puzzles. Due to poor AI implementation, the sidekicks, who were one of the game's selling points, became a focus of criticism. Tabs displaying the status of each sidekick are displayed on either side of the player's screen. When a sidekick moves too far away from the player their tab disappears. The player is also able to give the sidekicks commands such as Stay and Follow.

As the player progresses through the game they are able to level various attributes to improve their skills. These attributes are Power, Attack, Speed, Acro and Vitality.

Daikatana has a multiplayer mode which consists of two types of gameplay. Players can fight in a deathmatch style mode or race to collect treasure. In-game text chat is available in multiplayer mode

In feudal Japan, two rival clans, Ebihara and Mishima, are at war. Mishima goes to swordmaster Usagi Miyamoto to craft a weapon to end the conflict: the Daikatana. However, Usagi realizes Mishima's dark desires and gives the Daikatana to Ebihara; Inshiro Ebihara throws the sword into a volcano at the end of the war.