Previous Story:
Hayate was captured and became the subject of the experimental superhuman project (Project Epsilon). He was then left to die in the esoteric Black Forest of Germany. Even though he suffered amnesia, his deep desire to fight stayed intact with his beaten body. He mastered Karate in no time and became a Karate instructor. He then joined the "DOA2 World Tournament" hoping to regain memory of his past. He was known as Ein in DOA2.

DOA3 Story:
Hayate finally regained his memory after fighting in the last tournament. He now realises he is the brother of Kasumi and the best friend of Hayabusa. After he recovered his memory, he was officially ordained as the new leader of the Mugen Tenshin Tenjinmon clan. He is now set to enter the "DOA3 World Tournament" in order to defeat Genra, the superhuman created as a puppet of DOATEC's Project Omega.