After saving Izumo’s mom’s life and losing her own, Kotetsu’s mom’s dying wish was that her children are given her sword and that she be beheaded by the woman she gave her life for.
It’s a tradition among the Hagane and Kamizuki to kill one another for disappointing the other. Not only did Kotetsu’s mom feel like she disappointed her Kamizuki, she also didn’t want her head to be taken by the enemy forces that killed her (still ambiguous what type of mission it was that she lost her life on, or why or to who, but it happened when Kotetsu was only 2 months old)
So Izumo’s mom complied and decapitated her. (Maybe bringing her whole body back wasn’t an option since the team didn’t have any death scrolls on them or perhaps it was too badly destroyed?)
But that would be the last thing Kotetsu’s mom did in order to honor the bond she had with Izumo’s mom. Despite the arrangement being a massive power imbalance, these women loved each other like sisters- genuinely
Kotetsu’s sister, father and mother are all buried in the Tama-Hagane burial grounds just outside of Konoha
A plot of land has already been reserved for Kotetsu by Izumo’s mom. The burial site fees have already been paid in advance. Kotetsu found this rare, selfless act of kindness from Izumo’s mom as a silent display of threat or a promise that he’ll die by her hand one way or another…