No More Heroes
In No More Heroes, Shinobu is the 8th ranked assassin in the UAA. Shinobu is a high school student and tries to keep her life as an assassin a secret. She's so secretive about it that when Travis challenges her to a fight in front of her class, she kills everyone so that her secret is safe. After Travis defeats her by cutting off one of her arms, he spares her life and leaves her alone in the room they fought in.
Shinobu is not seen again until the end of the game. During Travis' final ranked match against his sister, Jeane, he suffers a near fatal blow when she stabs him through the chest with her hand. Shinobu arrives (arm intact) and cuts off Jeane's arm, repaying Travis for sparing her life and gives him an opportunity to defeat Jeane.
No More Heroes 2: Desperate Struggle
In No More Heroes 2, Shinobu is a playable character during a few segments of the game. She left America to become the number one ranked assassin in Asia, and comes back to America to help Travis get revenge for the murder of Bishop. She defeats New Destroyman and Million Gunman for Travis, then gives him double beam katanas before an awkward scene where she tries to bone him.