Takeo's sister is a character from Ju-on: The Final, portayed by Kanan Nakahara.
Biography
Her name is never mentioned, but she is Takeo's older sister. They apparently were not very close, and didn't interact much. They hadn't even met each other in years. At some point she met her husband and gave birth to Reo. They happily lived together in their house, and didn't even know of Takeo's and Kayako's deaths for a long time. At some point her husband died from unknown causes. Soon after that, she learned of Saeki's fate, and decided to adopt Toshio, who was thought to be still alive. This proved to be a fatal mistake.