According to Kayako’s ghost diary, the only way to defeat Utsushimi is to create a portal to the demon world:
The town is thrown into chaos as people begin acting strangely. It is revealed that they have been replaced by "mirror world" clones—evil counterparts created by the mirror ghost, . These clones can be identified by the glasses they wear and the fact that they cast no reflection. Satsuki and Hajime eventually find themselves as the last two "real" people in town who haven't been swapped. How to Seal the Ghost (Utsushimi) Ghost Stories (Dub) Episode 7
: Satsuki uses her compact mirror to reflect Utsushimi’s mirror. This creates a green-glowing portal that sucks in all the ghostly clones from across town, returning the original people to the real world. Memorable Dub Highlights According to Kayako’s ghost diary, the only way