Ashi is the deuteragonist of Season 5 of Samurai Jack. She was born and raised as a member of the Daughters of Aku with her six younger sisters. They served as assassins attempting to kill Jack. She later became the only surviving member and unwillingly accompany Jack. It was only later that she came to have doubts about Aku's true nature after Jack saves her life. She finally made a full turn-around when Jack showed her the destruction Aku has unleashed on the world and she saw all the good that the Samurai had done.
She served as Jack's most important ally in Season 5, in Episode XCIX she and Jack eventually fall in love. Eventually, after meeting Aku in person in Episode C, it is revealed that Aku was her biological father, after which he corrupts her unwillingly into his service. In Episode CI, she used her powers as a cambion to help transport Jack back to the past to defeat Aku but faded from existence on the day of her wedding to Jack as a consequence of past Aku's death.
Her character is given an alternate ending in the game, Samurai Jack: Battle Through Time, as she's still married to Jack and somehow avoided fading away from existence. She is with Jack in the final scene watching the horizon under the cherry blossom tree in a world free from Aku. The same cherry blossom tree Jack showed Ashi in Episode XCVI.