The mother of Ichigo Kurosaki who was killed trying to protect her son from Grand Fisher. She was a very loving mother and wife.
The Grand Fisher used the forms of humans whom he had devoured (mostly women) to attract other humans with high spiritual energy, and Ichigo, who at the time could not distinguish between ghosts and humans, saw Grand Fisher's lure and ran after it. Masaki, realizing this went after Ichigo and protected him from the Grand Fisher at the cost of her own life. According to Ichigo, Masaki was the center of the family and everything that went on with the family revolved around her. Due to this fact, Ichigo's family was greatly devastated by her loss.
They visit her grave every year, and that is the only day in the year Isshin smokes. The reason he smokes in front of her grave was because when they had first started dating, Masaki complimented him about how cool he looked while smoking. He also added that was the first and last time she complimented him about his appearance. Isshin hung up a large poster of her in his home, displaying the phrase "Mazaki forever".
According to Tatsuki Arisawa, Ichigo stopped crying every time he saw his mother. She claimed Ichigo had the most beautiful mother ever, and took it upon himself for her death. Isshin also thought it was his fault his wife died. He says this the reason being he couldn't get there in time to protect her from the Grand Fisher. When Ichigo asked him why nobody ever blamed him for his mother's death, Isshin explained to him that "he was the man the woman I fell in love with gave her life to save." He also added that when they meet each other again, if he had ever blamed Ichigo, Masaki wouldn't be able to forgive him.
She is a quincy and was adopted into the Ishida family.