- "I'm impressed. I didn't expect you to make it this far."
Isako was the leader of the Katakuri Ninja Clan that operated out of Inotakimura, Japan. She and her clan serves as killers for the Director and H.A.R.M., primarily out of duty than a sense of allegiance. The Director has stated to dinner guests that he must manipulate Isako much like a little dog (much to the anger of some of the clan members) but also recognizes her honor and competence in his happy birthday note he wrote to her (as later found by Cate Archer).
In her earlier years, Isako was alone on the streets of Kyoto (after her parents had been murdered) when she was found by an old woman and her daughter (whom at the time was the head of the Sakuragaoka Ninja Clan) where Isako was trained in the ninja arts. When Isako turned 14 years of age, she was sent on her first mission. She was tasked with killing a merchant who was kidnapping girls to turn them into prostitutes for his gambling dens. However the mission was a trap set up by the man who hired the ninjas for the task and Isako was captured before she could complete the assassination. Before the merchant could dispose of Isako, his European friend (The Director) asked if Isako's life could be spared so that she may work for him. Thus the deeply honorable Isako felt she owed a great debt to The Director. She turned down several offers to betray The Director out of this sense of duty.
Isako was given the task to kill Archer in Japan, but Archer survived the stab wound. When it was discovered that Archer had survived, Isako and her ninja clan was sent again to complete the task tracking her down to Akron, Ohio. Isako's ninjas swarmed the home of Melvin Blitzny and flushed Archer out to the nearby Serenity Valley Trailer Court where Isako confronted her once again. The two battled in a Mobile Home that had been picked up by a Tornado. Archer was able to rebuff the attack and Isako escaped by using her Umbrella to fly off into the storm.
After Isako had failed a third time to kill Archer, she has fallen from grace in the eyes of her master. When The Director tried to shoot Isako for her failure, Cate Archer saved her life by disarming the villain. Thus freeing Isako from her bonds of honor to H.A.R.M. In order to re-pay her debt to Archer, she agreed to stop trying to kill her (symbolically breaking her Katana in half).
Isako's primary weapon is the Katana. She had one of these swords hidden in the handle of her umbrella. She was also able to use this umbrella to ride out the winds of a tornado. Isako is also skilled with the use of the Shiriken and the ninja Smoke Bomb. Isako could jump high distances when needed.
- Isako is voiced by Jen Taylor who also voiced main character Cate Archer.