Resonance

In Fatal Frame IV, Resonance is one of the advanced stages of Moonlight Syndrome. At this point, the victim's symptoms do not only afflict them, but also begin to have an effect on those who come into contact with them. It was observed that patients who already have Moonlight Syndrome will deteriorate if they look upon the face of someone during the Resonance stage. Prolonged contact with a patient at this stage can cause others to become mentally ill themselves, or to commit suicide. Resonance appears to cause conflicted reactions among people nearby; some will be drawn to gaze upon the patient's face, while others will be afraid to do so. This is similar to the conflicting feelings of religious taboo and attraction associated with the Mask of the Lunar Eclipse.

When a patient is resonating, characters exposed to them will often remark that they cannot remember the patient's name or what they look like, or alternatively that their name and face are constantly changing. This instability is a reflection of the fractured identity and damaged Moonsounds caused by Moonlight Syndrome.

Resonance is the mechanism by which Sakuya Haibara spread her blossoming to everyone on the island on the Day of Tranquility. It is also possible for an Vessel to resonate in her trance state during the Kagura or Rite of Descent, and infect those present.

According to the lore of the Guardians, the moon also resonates when it is troubled, and this is the ultimate cause of Blooming. The only known remedy is the Moonsong.