Dead or Alive
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A game called Dead or Alive: Code Chronos was in development for the Xbox 360. The game would have been a prequel to the series and would relay the story of Ayane and Kasumi before the first tournament. However, the progress of Code Chronos came to a halt due to Itagaki's dispute with Tecmo. In 2010, the project was then confirmed canceled by the current head of Team Ninja, Yosuke Hayashi.

A promotional image advertising Dead Or Alive 4 featured an ad for Code Chronos in the bottom-right corner.
Contributed by DrakeVagabond
The series gets it's name from a wager that the lead programer, Tomonobu Itagaki, made with the head of Tecmo. Itagaki assured the president he would create a video game that would garner a competent fan base. He named the series "Dead or Alive" to demonstrate that the company's future rested on the game's success.
Contributed by gamemaster1991