Ein

Ein (アイン, Ain) is the "alter ego" of Hayate, who first debuted in Dead or Alive 2. After being used as a test subject by the Dead or Alive Tournament Executive Committee for Project Epsilon, Hayate gained amnesia and trained in the art of karate, going by the name of "Ein." By entering the second Dead or Alive Tournament, he was able to regain his lost memories and became Hayate once again.

After his appearance in Dead or Alive 2, Ein was replaced by both his real identity Hayate, and Hitomi, a friend of Ein who shares the same martial arts style, Karate. Despite Hayate being Ein only temporarily, this persona has become a recurring unlockable character in the rest of the Dead or Alive games following his first appearence.

The Second Tournament
Just before the second Dead or Alive Tournament, Hayate was kidnapped by Kasumi Alpha, a science product of the Dead or Alive Tournament Executive Committee. He became the sole subject for Project Epsilon, created by Victor Donovan and lead by Lisa Hamilton, which was suppose to turn him into a superhuman weapon.

Hayate was kept at DOATEC Germany and the project team managed to repair Hayate's spinal cord and bring him out of his death-like coma (which he entered after being seriously injured by Raidou). However, before they could continue, Ryu Hayabusa attacked the German headquarters to save Kasumi, who was being held captive in the same building.

Hayate was placed onto a helicopter with Lisa to be taken to another DOATEC lab but the engine failed and the helicopter crash-landed in the. Although wounded, Hayate got away from Lisa and was lucky enough to stumble into a clearing where Hitomi was training Mistaking her as Kasumi before collapsing.

As a result of the traumatic events, Hayate gained extreme amnesia and couldn't even remember his own name. While he was staying with Hitomi and her father, he was named "Ein" and worked in the family's dojo, mastering karate in a short period of time.

Wanting to find out who he was and where he came from, Ein entered the second tournament on a journey of self-discovery. Along the way in the tournament, Ein met up with Ryu and Ayane (Hayate's best friend and half-sister), who both wondered if he is really Hayate and Helena Douglas, who talked about the failed Project Espilon, which confused Ein.

After the second tournament, Ein finally met up with Kasumi, Hayate's younger sister and, following Ryu's advice, they battled each other. Although Kasumi was defeated, Hayate finally remembered who he was.

Appearance
Also see: Ein's Outfit Catalogues

Personality
Ein's personality is somewhat similar to Hayate as he seems to be reserved and quiet. However, Ein also seems ignorant at times; he would rather fight than converse to find out answers.

Like most fighters in the series, he is skilled and dedicated to his style, with a great understanding of martial arts even though his conscious memory did not return. If he was not, Hitomi would not have sought him out in order to help rebuild her father’s dojo. Most times, especially in Dead or Alive Ultimate, Ein prefers to just fight than talk with his opponent. In his spare time, Ein practices breaking bottles with his hand by slicing the tops of them off in a demonstration of skill and entertainment.

Etymology
The name "Ein" likely comes from "eins," the German word for "one" or "first." It's been noted that the letters of "Ein" are also the first, middle, and last letters of Epsilon. Whether or not this was intentional remains to be seen.

Hitomi
After the first tournament, Hayate was found in the Black Forest of Germany by Hitomi, whose family took him in. After being used for the Epsilon Project he suffered from amnesia, he could not remember his past or even his name and ended up going by the name of "Ein." The two of them trained together under her father but Ein soon departed for the second Dead or Alive tournament, where he recovered from his amnesia. After this, Ein remembered who he was and left for the Mugen Tenshin Ninja Clan.

Helena Douglas
In the second tournament, Ein meets Helena Douglas who confused the amnesiac Ein by talking to him about the Epsilon Project but he didn't remember anything about it. In the end, they fight and Helena was defeated by him.

Kasumi
After the second tournament, Ein finally meets up with Kasumi, Hayate's younger sister and, following Ryu's advice, they battled each other. Although Kasumi was defeated, Hayate finally gained back his memories.

Ayane
Ayane found Ein who instantly recognized him as Hayate. However, since Hayate still lost his memory, Ein fights Ayane.

Ryu Hayabusa
During the second tournament, Ein fought Ryu and started to remember who the ninja is. When he met Kasumi, he followied Ryu's advice to battle Kasumi; after defeating her, Hayate finally gained back his memories.

Gameplay
Being the predecessor to Hitomi, Ein is a medium-damage strike character with excellent high-position combos (F, Y or Tsubauchi). He's best played from an aggressive standpoint, where he can position himself close to the enemy. However, a weakness shared between the two is the slight "wind-up" timeframe needed prior to the execution of attacks.

Unlocking Ein
Ein is an unlockable character in Dead or Alive 3 and Dead or Alive 4, in which he can be used in every gameplay mode except Story Mode. To unlock him:
 * Dead or Alive 3: Finish Story Mode with every character then play Survival Mode with Hayate, getting enough victories so you can put your name in the rankings. While at the ranking screen, enter EIN as the name.
 * Dead or Alive 4: Play through Hitomi's Story Mode.

Dead or Alive Series

 * Dead or Alive 2 (1999 - 2000)
 * Dead or Alive 3 (Unlockable character, 2001 - 2002)
 * Dead or Alive Ultimate (2004 - 2005)
 * Dead or Alive 4 (Unlockable character, 2005 - 2006)
 * Dead or Alive: Dimensions (2011)
 * Dead or Alive 5 Ultimate (2013)

Musical Themes

 * Vigaku - Dead or Alive 2, Dead or Alive 3, Dead or Alive 4, Dead or Alive: Dimensions, and Dead or Alive 5 Ultimate

Trivia

 * Unlike other alter-egos in other games such as Devil Jin, Wild Iori, Evil Ryu, Mu-12, or Siegfried version of Nightmare, Ein doesn't possess any kind of evil.
 * Even though Team Ninja wanted him to be in the fifth title, he was cut because of time constraints. He returns in Dead or Alive 5 Ultimate.
 * His theme Vigaku can be heard in the Dead or Alive 5 story at the beginning of Mila's chapter when Tina enters the diner.
 * Ein's hobby of slicing the tops off of bottles with his bare hands is likely a reference to a scene from The Karate Kid, where Mr. Miyagi performs the same feat.
 * Ein and Hayate share tag poses and a tag move for the first time in Ultimate. Ein's skin is also slightly different, more like his colour in Dead or Alive 2 to Dead or Alive 4. It can be more noticeable in their faces in the win pose.
 * Ein and Lisa share a tag pose in Dead or Alive 5 Ultimate. The tag pose seems to relate to the period in which Lisa was involved in the experiments done to Ein.
 * It's possible that Hayate still uses his Ein persona on occassion if the tag responses with Ein and Hitomi in Dead or Alive 5 are accurate.