Shadow

Shadows are mysterious entities that exist as a counterbalancing force in the Afterlife, manifesting themselves when a certain condition is met. Their only purpose is to take over the Afterlife and attempt to "reset" the amount of love that has been manifesting in the Afterlife, consuming humans and even NPCs in the process.

The Shadows serve as the main antagonists of the anime series.

Appearance
Shadows were dubbed by Yuri based on their physical form. The Shadows look like large slightly humanoid clouds of dark colored matter with small white orbs as eyes, with arms appearing on either side. They have reflexes surpass that of humans. They appear to be connected to the ground, but are revealed to have leg-like structures from when they leaped onto Otonashi, Hinata, and Naoi. They can be disintegrated by being repeatedly attacked, such as with normal caliber bullets (less than .30 cal), but are shown to be weaker to bladed weapons or higher caliber bullets (greater than or equal to .30).

Purpose
They are programmed to absorb humans in the Afterlife, consuming their soul, and change them into NPCs, in which they envelop the target and slowly drag them into the ground. The first appearance was manifesting itself from Naoi's shadow, but the first victim to be changed was Takamatsu. The next moment the target is seen, he or she will act as an NPC, attending classes. The victim will also not remember anyone they know in life or what happened to them. This was the case for Takamatsu, whose soul was consumed by the Shadows, was puzzled when Hinata said he was swallowed by a Shadow.

Humans that were absorbed or changed can return to their normal form once the controlling influence of the reset program is removed, or if they have a strong enough will which both Yuri and Takamatsu showed.

Trivia

 * When Otonashi and Hinata first encountered the Shadow, it took several bullets to take one down, but during the main invasion (after the disappearance of most of the SSS) it took only one bullet to effectively "kill" one.
 * After the credit sequence of Episode 10, there is a clip of Noda killing a shadow that attacked Ōyama and afterward asks "Wh... What the Hell did I just kill?” Yuri then receives a report from Yusa explaining the situation.
 * Whether or not the Shadows were created by the Programmer, or had existed before he arrived remains a mystery, however, information does lean towards the possibility that they were likely to be creations by the Programmer.