The Coming of the Quantum Cats can - given different social conditions - develop completely different character traits (timid or assertive, benevolent or predatory, etc.) The title refers to the famous thought-experiment known as "Schrödinger's Cat", where the outcome of a real-world event depends on a quantum event. By some interpretations, the real-world object, in this case a cat, must be in two states simultaneously until it is observed. However, the story is more closely related to the many-worlds interpretation of quantum mechanics where all possible outcomes of an event occur, each in its own parallel universe. The same concept was treated, somewhat more pessimistically, in
Dead or Alive 5 as several new stages and fighters (including "Ninja Gaiden"s Rachel and Momiji, and "Virtua Fighter"'s Jacky Bryant, as well as the return of "Dead or Alive 2" characters Leon and Hayate's amnesiac karateka identity, Ein), and all-new features such as two-on-two online multiplayer tag team battles, among many other changes. Three new female characters: Marie Rose, Phase-4 and Nyotengu, joined the game's roster in 2014. A free digital version, titled "Dead or Alive 5 Ultimate: Core Fighters", which features four playable characters and the online mode, with additional characters and story mode content available as purchasable downloadable content, was released