Mieko Murasako is the spouse of Hidemasa Murasako. She is said in episode 2 to have have gone to the Ozaki clinic, and told them that her husband was ill with a summer cold.
Her body was found in her home by Seishin on August 6. Oddly, when found, her body is still fresh, although her dead husband found alongside her is badly decomposed after laying dead for several days. They presume that she died August 5. According to the autopsy, Mieko died of natural causes.