In addition to being Isshin's wife and Ichigo's, Karin's and Yuzu's mother, she was also the mother-in-law of Orihime Inoue, and the paternal grandmother of Kazui Kurosaki.
She is voiced by Sayaka Ohara in the Japanese version of the anime, and by Ellyn Stern in the English version of the anime.
Masaki was described by Ichigo as being the center of the family's universe. She was a very good woman and was always cheerful since Ichigo mentioned that he never saw her get angry or sad. Ichigo's female friend, Tatsuki, also mentioned that whenever Masaki came to pick Ichigo up from his classes, he would always have a big smile on his face.
During her life, Masaki greatly enjoyed spending quality time with her husband and children. She was very protective toward her children, and she even risked her own life to protect her son when he was trying to rescue the girl by the river. This trait was pasted down to her son which gave Ichigo the determination to protect those he loves.
Masaki was born on June 9. When she was a teenager, her parents died leaving her to be an orphan thus becoming the last member of the Kurosaki family. She was eventually taken in by Ryuken Ishida's mother so that she would be protected as one of the last Quincy so that one day she would marry Ryuken Ishida to keep the Ishida bloodline pure and keeping the Quincies from becoming extinct. Her adopted mother had scolded her at least once because of her slow training progress. Masaki sense hollow fighting with Shigami named Isshin Shiba at hallway, Masaki rushed to recuse him by using blut and allowed Hollow to bite her before Masaki manged to kill the black hollow in front of Isshin it was late for Ryuken and Katangi who come to fight Hollow. Masaki and Isshin meet at first time and incudtion each other for their idenites
Years later, she eventually married Isshin Shiba together they had three children. After Karin and Yuzu were born, her eldest son Ichigo took martial arts classes so that he can become stronger and protect both his mother and sisters. Masaki always came and picked up Ichigo from his classes.
On June 17, one month before Ichigo's tenth birthday, Masaki was picking the 9-year-old Ichigo up during a rainstorm and Ichigo noticed a young girl near the river as if she wants to jump in. Ichigo let go of his mother's hand and ran over to save the girl with his mother running after him and yelling him to stop until everything went black. Ichigo woke up to find his mother on top of him severly wounded and dead with Ichigo not knowing what really happened to her.
Every year on June 17, the Kurosaki family would visit Masaki's grave to pay her their respects. Six years later, it was revealed that Masaki was really killed by a hollow named Grand Fisher who kills children (women in the anime) and that the girl was actually Grand Fisher's antienna bait to use as a lure for his victims.