After her brother Hayate was almost killed by Raidou, a crazed ninja who had been expelled from the village, Kasumi took over as the eighteenth head of the Mugen Tenshin Clan. But in her breast burned only the flames of vengeance - she longed for revenge on the man who had taken her kind and strong brother from her, and who had stolen the village's greatest treasure.
Knowing that any ninja leaving the village was considered a traitor and would be punished with death, Kasumi nevertheless snuck out in pursuit of her adversary, eventually finding herself at the Dead or Alive fighting tournament.
Under the watchful gaze of her half-sister Ayane, sent to secretly follow her, Kasumi defeated Raidou. But no sooner did she claim victory than a mighty explosion ripped Raidou's body to shreds, leaving Kasumi herself nowhere to be seen...
Following the tournament's conclusion, it was revealed that its main sponsor Fame Douglas had been assassinated. The various participants went their separate ways, as the whole event became shrouded in a veil of mystery and uncertainty.
It was revealed that having disappeared at the end of the first Dead or Alive tournament, Kasumi was in fact abducted by DOATEC as the test subject for something known as Project Alpha. She managed to escape, but on her way out she encountered her clone, Alpha. Smiling cruelly, Alpha told her, "Hayate is mine."
As all this was happening, the second Dead or Alive tournament was announced.
Dragon Ninja Ryu Hayabusa, a friend of Hayate's, immediately sensed that a great evil beyond human comprehension was involved. "This is no ordinary fighting tournament," he declared, and set off in an attempt to save the world from destruction.
At the same time, Hayate disappeared from his deathbed, kidnapped by agents from DOATEC to be a test subject for Project Alpha's successor, Project Epsilon. However, an accident during transportation luckily freed Hayate from DOATEC's clutches.
Suffering from amnesia, Hayate was taken in by Hitomi, a karate expert who happened to be training nearby. Once his wounds healed, he found himself drawn inexorably to the Dead or Alive tournament, entering under the name of Ein...
Having regained his memory, Hayate returned to his rightful post as the eighteenth head of the Mugen Tenshin Clan. At the same time, however, the Hajin Mon sect of the clan was in turmoil. The sect's leader, Genra, had been abducted by DOATEC and turned into an inhuman monster as part of their latest plan, Project Omega.
Eventually, it was announced that the third Dead or Alive tournament was to be held. The true purpose of the tournament, however, was to give Victor Donovan, the true power behind DOATEC, an opportunity to test the monster he had created as part of Project Omega.
To Ayane, Genra was both her adopted father and her teacher, and now he had been transformed into an inhuman killing machine. It was her duty as a good daughter to right the wrongs of her father, and to grant him peace.
DOATEC's repeated experiments using human bodies had brought about one tragedy after another. The anger felt by the ninja toward this soulless corporation had reached breaking point.
Taking over from her father as head of DOATEC and striving to follow the principles and ideals he held dear, Helena Douglas announced that she would hold the fourth Dead or Alive tournament.
However, the rage felt by Hayate, head of the Mugen Tenshin Clan of ninja, soon turned into flames that would consume the 999 meter-high DOATEC TriTower, a symbol of the power and greed of the mighty corporation.
But just as the flames licked at the foot of the towers, the final result of DOATEC's ungodly experiments was being born: the ultimate fighting machine, Alpha-152.
The ideals and principles of Helena's father Fame Douglas had been utterly destroyed by the treachery of Donovan and the enmity his acts had brought to bear.
Realizing that her own idealism and naiveté had given rise to the terrible Alpha-152, Helena took the only course of action she knew was right. She would remain in the towers, and destroy them from within.
Surrounded by flames, and with the towers on the verge of collapse, Helena was suddenly and unexpectedly rescued by Zack, swooping in with his helicopter. Stunned, she looked back just in time to see the ultimate symbol of DOATEC crumble to dust.
2 years after the destruction of the Tri-Towers, the symbol of DOATEC.
DOATEC's leader, Helena Douglas, carries on the wishes of her late father and founder of DOATEC, Fame Douglas, endeavoring to restore the organization.
The Super Human Development Project, led by the mad scientist Victor Donovan, freezes and then dismantled.
The organization has reached its goal of cleaning up its activities... or so it looked.
But Donovan's ambitions did not cease and he continued to work behind the scenes.
M.I.S.T.: a new organization that carries on the advanced biotechnology of DOATEC
Under this new organization, Project Alpha, which used the DNA of Kasumi, kunoichi and a successor of the legendary Mugen Tenshin ninja clan, was moving forward into its next sinister phase.
The 5th DEAD OR ALIVE Tournament announcement from Helena, which was meant to show the bright rebirth of DOATEC to the world, was instead becoming a warning to the rise of the worst nightmare to humankind....