This page contains MAJOR spoilers for The Fifth Division in the Red (Story Arc), Princess on Vacation, and Soul of Shirahime.
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Throughout her incarnations, Shirahime had twenty-six children with Shiroyuki. She also considers Kosetsu her son and claimed Nemu as well. Uryu occasionally calls her “mom” due to her relationship with his father, but he does not consider her children his siblings, and neither do they.
Her first child was Princess Hikari, daughter of Shirayukihime and Crown Prince Ichigo. Crown Prince Shiroyuki (the reincarnation of Crown Prince Ichigo’s twin brother, Kail) later declares himself as Hikari’s father instead of Ichigo. Hikari is later incarnated as Yachiru Kusajishi.
The twins Matsuri and Fujimaru were children of an unknown incarnation and died when they were very young, three-years-old in human terms. They were later reincarnated as Matsuri and Fujimaru Kudo and adopted by Seigen Suzunami. Shirayukihime’s incarnation Yukihime Suzunami was Seigen’s wife, but he did not acknowledge her as their mother.
Shirahime Thorne or a prior incarnation had the twins Daichi and Raiko. Shirahime hid Raiko inside of Daichi to protect her from her biological father. Eventually, some shinigami find out that their biological father is Sosuke Aizen, but it is a forbidden topic in Soul Society.