Crossover

A crossover is where two franchises converge in a single game belonging to one of the two franchises. Dead or Alive has engaged in several crossovers with various video game franchises since Dead or Alive 4. Crossovers can involve guest characters hailing from that franchise or having various elements specifically originating from another franchise. Note that Ninja Gaiden references do not count as crossovers due to both Ninja Gaiden and Dead or Alive explicitly taking place in the same universe.

Dead or Alive 4
The character SPARTAN-458, real name Nicole, although technically originally created for the game, hailed from the Halo franchise, with it being explained that she and her home stage, Nassau Station, being pulled through a time wave to the past. She eventually appeared as sort-of canon in later entries of the latter franchise.

Dead or Alive Paradise
Rio of Super Black Jack acted as a guest character for the game, where she was a blackjack dealer for Zack Island as well as an unlockable character.

Dead or Alive Dimensions
Samus Aran and Ridley, alongside the Geothermal Power Plant from Metroid Other M, appeared as hazards and a stage respectively in the game.

Dead or Alive 5/Ultimate/Last Round
The Virtua Fighter characters Akira Yuki, Sarah Bryant, and Pai Chan appeared in Dead or Alive 5 as well as its expansions, with Akira and Sarah in particular playing minor roles in the story mode (specifically, having a sparring match with Kokoro and Zack mistaking the latter for Tina Armstrong, respectively). Sarah's brother Jacky Bryant also appears in Ultimate. Aside from Virtua Fighter, the characters Naotora Ii from Samurai Warriors and Mai Shiranui from King of Fighters also crossed over with Dead or Alive in Dead or Alive 5 Last Round, with there also being themed crossover DLC costumes from their respective franchises upon their debut.

Aside from playable characters from the above franchises, there was also a DLC stage derived from the anime Attack on Titan, complete with a matching DLC collaboration costume set, as well as DLC costumes based on Senran Kagura, Warriors Orochi 3, the Deception series, Wakaki, Falcom(R), Schoolgirl Strikers, Tatsunoko anime franchises, Gust, Fairy Tail, Aquaplus, and Arc System Works.

Dead or Alive Xtreme 3
The DLC for Dead or Alive Xtreme 3 included crossover outfits from both Senran Kagura and Keigo.

Dead or Alive Xtreme Venus Vacation
Dead or Alive Xtreme Venus Vacation had crossed over with Destiny's Child, The Melancholy of Haruhi Suzumiya, and Is It Wrong to Try to Pick Up Girls in a Dungeon?, featuring themed SSR outfits for each one. Of the crossovers, only the Destiny's Child crossover is given a direct acknowledgement in-universe, as the character Tamaki was mentioned to have been inspired to create the specific outfits for Marie Rose, herself, Misaki, and Kasumi (based on Davi, Mona, Liza, and Eve, respectively), as well as material based on due to a broken TV set mysteriously turning on. The latter collaboration, titled Is it wrong to ask for a meeting on vacation?, also featured exclusive Owner Room apparel such as a projector screen featuring clips from the titular anime (which is implied from the Warner Bros logo being seen to be the English dub for the anime) as well as life-sized posters of the characters Hestia, Lilika, and ICE and a movie poster for Orion Arrow.