He was played by several child actors, being Ryôta Koyama in the original two V-Cinema movies, Yuya Ozeki in the theatrical movies and the first American remake The Grudge, Ohga Tanaka in The Grudge 2, Shimba Tsuchiya in The Grudge 3 and Daiki Sawada in the short movie "4444444444".
Toshio is a child who was murdered by his father along with his mother Kayako Saeki. This led to them becoming evil spirits. His mother then killed his father in revenge leading to him becoming an evil spirit as well. The three of them then haunt anybody who enters the house.
Unlike his parents, Toshio rarely kills anyone, but prefers to haunt them. His knee victims are Jennifer Williams and Matt Williams, who he was seen suffocating to death in The Grudge as well as killing Sally and Trish in The Grudge 2. He also murdered Mr. Praski off-screen in The Grudge 3 and possibly the man from 44444444444. In the second movie, he pulled Aubrey Davis into the house, causing her to be cursed.
- Toshio's first appearance was in Takashi Shimizu's short movie "4444444444".
- Toshio is often characterized by his pitch-black eyes, pale skin, and the haunting meowing sounds he makes.