Toshio Saeki is a fictional character from the Ju-on franchise, created by Takashi Shimizu. He was played by several child actors, including Daiki Sawada in the short movie 4444444444, Ryōta Koyama in the original two V-Cinema movies, Yuya Ozeki in the theatrical movies and The Grudge, Ohga Tanaka in The Grudge 2, Shimba Tsuchiya in The Grudge 3, Shūsei Uto in Ju-on: White Ghost and Ju-on: Black Ghost, Kai Kobayashi in the 2014 Japanese reboot Ju-on: The Beginning of the End, and Garrett Masuda in the parody Scary Movie 4. He is characterized by his pitch-black eyes, pale skin, and the haunting meowing sounds he makes.

Katasumi and 4444444444 are two 1998 short Japanese horror films both directed by Takashi Shimizu, forerunners to the Ju-On franchise.