The Hashiras got to the Mansion when it was attacked. They found Kagaya, Amane, Hinaki, and Nickika dead. But along the ruins, lay y/n, also known as Okasan, Kagaya’s little sister and the Hashiras mother figure. The Hashiras had already killed Muzan ans the demons. They all were alive, but while killing the demons, y/n lauded on the ground suffering through pain and wounds. When the demons were all killed, the Infinity Castle fell and the Hashiras returned to the Ubuyashiki estate.