Kasumi is the daughter of Ayame and Shiden, the 17th leader of the Mugen Tenshin Clan. She has an older brother named Hayate and a half sister named Ayane. It is unclear whether or not she knows of her relation to Ayane given the circumstances surrounding Ayane’s birth. From childhood Kasumi lives the privileged life full of expensive clothes, servants, and the respect of the rest of the Mugen Tenshin Clan. Being that it was a ninja clan she also trained hard along with her brother who she had a vary close relationship with.
Raidou Kasumi’s uncle Raidou, who had been banished from the clan years ago, returns to the Mugen Tenshin village to steal a secret move called the Torn Sky Blast. Hayate and Ayane fight Raidou and Hayate uses the torn sky blast in the fight, thus showing Raidou how it’s preformed. The fight ends with Raidou using the Torn Sky Blast and putting Hayate in a coma. After realizing her brother might never wake up Kasumi abandons the clan to take vengeance on her uncle for what he did to her brother. The clan brands Kasumi a runaway shinobi and tasks Ayane with eliminating her. Kasumi learns that her uncle is involved with a company called DOATEC and enters a fighting tournament they are hosting. Unbeknownst to Kasumi, while she is participating in the tournament the still comatose Hayate is kidnapped. Kasumi makes it to the final round of the Dead or Alive 1 World Combat Championship and faces her uncle. She kills him and wins the tournament. Immediately afterward she is taken captive by the Super-human Development Project.
While Kasumi is held captive her clone ‘Kasumi Alpha’ is created. Kasumi is entered in DOA 2 and faces her clone. Kasumi defeats the clone and advances. During the tournament she sees Hayate, but he has amnesia and doesn’t recognize her. Later she faces off against Ayane who was sent by her clan to kill the traitor. Kasumi wins the fight and escapes again.
Kasumi joins DOA 3 in hopes to see her brother who has regained his memory since the last time they met. She does find him but the reunion isn’t what she had hoped. Being that Hayate is now the leader of the clan she abandoned, he cannot show lenience towards Kasumi. Kasumi wins in the tournament and returns to a life on the run from her brothers clan.
Kasumi receives an invitation to DOA 4 but when she arrives to the island it’s supposed to be held on she discovers it was a rouse by Zack. Still, a free vacation is a free vacation and she tries to enjoy herself. Despite the fact that Ayane is also there, Ayane makes no attempt at killing Kasumi.
After vacation Kasumi enters the real DOA 4. While there she discovers that DOATEC has crated a new version of Alpha named ‘Alpha-152’ that is designed to be a super-human. Alpha-152 and Kasumi fight while stories above them the tower they’re in is being destroyed by Hayate and Ayane. Kasumi defeats Alpha-152 escapes with her life before the building explodes.
Some time later Zack becomes a billionaire once again and vows to rebuild DOATEC to “bring peace to the galaxy.” He then sends out invitations to DOA 5. Kasumi goes thinking that she’ll be able to see Hayate there. It winds up being another girls only vacation and once again Ayane contains herself from killing Kasumi, if for no other reason than that it would ruin the vacation for everyone else.