Grand Fisher, a Hollow 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 souls and humans, saw Grand Fisher's lure and ran after it. Masaki, realizing this went after Ichigo and protected him from 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 "Masaki 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 could not get there in time to protect her from 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 would not be able to forgive him.
Agent of the Shinigami arc Edit
When the Kurosaki family visited Masaki's grave, Grand Fisher returned as he could sense their high spiritual power. During the fight, when Ichigo began to lose, her memory upon being killed was released from Grand Fisher's lure, telling Ichigo her last thoughts before she died. All she could think about was how much fun they all had together, and for Ichigo to never stop smiling. Her spirit gave Ichigo the strength to nearly kill the hollow, forcing him to escape.
The New Captain Shūsuke Amagai arc (anime only) Edit
Note: Events occurring in this arc are only in the anime and do not constitute canon material.
Masaki Kurosaki reappears when Ichigo Kurosaki faces off against Hanza Nukui. Hanza Nukui uses his Bakkōtō, Saiga, to look into Ichigo's memories, and then tortures him with the memories of the death of his mother. Hanza makes it so she tries to choke Ichigo, making it so Ichigo can't harm her or fight back. Before Ichigo chokes to death, the pleasant memories with his mother comes up from deep within him. A twister of Reiatsu surrounds them.
Ichigo then tells his mother how much everybody misses her, and he manages even without her. Before she vanishes, she smiles after Ichigo thanks her for protecting him that day.