Bill Pullman's character serves the plot in the same way that Yurei Yanagi's character did in 'Ju-on'. Also, without giving too much away, the jaw scene is taken directly from 'Ju-on'.
The ghouls portrayed in the film are often seen standing still in the background, mouths agape - an homage to Toshio in "Ju-On: The Curse". Also, one of the mirror ghouls at the end is a child, and a spitting image for Toshio, down to the makeup.