Phobia

Phobias are a race of supernatual spirits that seek to drive people into committing suicide. There is a group of more powerful Phobias, called Megalophobias, which have special abilities.

Overview
Phobias are malignant spirits that amplify a person's negative emotions until they commit suicide. They are responsible for almost all suicides in the world, with only a tiny minority of suicides happening without them. They attach themselves to people that experience hardship and pain, where they push them into killing themselves.

Phobias appear to be born in a parallel world, referred to by Manten as the Suicide Forest, where the souls of suicide victims turn into trees. Here, Phobias develop inside clear eggs until they mature and are unleashed upon the human world. A Phobia can become a Megalophobia by killing a Suicide Girl.

Suicide Girls are tasked with killing Phobias to prevent their proliferation. A significant weakness is that whenever a Phobia kills someone, there is a window of time, lasting 4 hours, 44 minutes and 44 seconds, where if the Phobia is killed, time rewinds to a short time before the person's death - only Suicide Girls, the Manager and other Phobias will retain their memories.

Appearance
Phobias have unique appearances, but most of them are vaguely humanoid with a corpse-like body, dry and stiff, but sometimes they have more animalistic characteristics such as horns, beaks, wings and snouts. They tend to not have eyes and their mouths are stitched shut.

Imperceptibility
Phobias are normally invisible and intangible. Only Suicide Girls can interact with them.

Negative Emotion Amplification
When a Phobia attaches itself to someone, they feel a dramatic increase in sadness and hopelessness, which will grow indefinitely until they kill themselves, whereupon the Phobia will move to a new target, usually someone negatively affected by the first target's death, such as a family member.

Strength and Speed
Phobias are shown to also be extremely strong and fast as shown during Kirari's fight.

Trivia

 * The time limit for undoing a Phobia's kill (4h 44m 44s) is a reference to how in Japan the number four (し) is associated with death (死), because both words are pronounced the same way, shi.