Childhood Radiation

"First, a certain man will steal capsules from a certain land. These capsules contain incredible power. Activating the capsule requires a special energy. It's spread throughout the universe, circulating within planets and lifeforms. In order to gather this energy, the man created a certain material. He names this material the Carellen element. But its only stabilize within the bodies of living creatures. The man disperses the Carellen element about, which lets him use living things to cultivate high-density energy. This energy, which tends to circulate planets and lifeforms, is known as Childhood Radiation."

- Kei Fukuide, The Geed Identity.

Childhood Radiation (幼年期放射) is an energy matter which first appeared in Ultraman Geed.

Nature
The Childhood Radiation is in fact a raw form of energy which can only be cultivated within life forms. Once dominated within a life form, they would form an energy sphere called Little Star (リトルスター) as their host would experience symptoms such as hand feverish, energy radiation from their chest and development of powers (which strangely corresponds to an existing Ultra Warrior). This as well puts them at risk since most Kaiju are capable of tracing their lights and attracted in a similar manner to bugs. Among the ways to separate them are through wishes upon an Ultra Warrior and strong emotions.

Carellen Element, a material which Kei developed served as a magnet to Childhood Radiation and is a major key in the development of Little Stars. The Childhood Radiation plays a crucial part in the activation of Ultra Capsules. Once entering an empty Ultra Capsule, an image of its corresponding Ultra Warrior would appear.

Pre-Ultraman Geed
The Childhood Radiation was in fact Ultraman King's own essence that spread across the universe after assimilating with it to reverse the effect of Crisis Impact.

Having stole the Ultra Capsules in the Land of Light, Kei Fukuide realized that the activation of these devices requires the Childhood Radiation. Kei created the Carellen Element as a magnet for the energy essence and had them cultivated within Earth life forms. Little did he knew is that Laiha Toba developed this symptom earlier than anyone else as she was rescued by Ultraman King during her birth.

The first attempt to harvest Little Star began six years before the start of the series as Skull Gomora rampaged in the Mt. Mitsuse and provoked Laiha by killing her parents. However, it caused the opposite outcome as her Little Star was suppressed by her grief and Kei simply walked off, unintentionally exposing himself.

Ultraman Geed
The rest of the Little Star symptoms by the present day. Kei instigated a chain of events that would led the clone of Ultraman Belial, Riku Asakura to take up the mantle of Ultraman Geed and portray the role of hero. As Geed becomes the image of a hero, Kei watched from afar as future monster attacks (either by his own or other circumstances) would help the Ultra in collecting Little Stars as Ultra Capsules.

As of episode 16, AIB decided to take the Little Star cases into their matters, such as developing enzymes that would dissolve the Carellen Element and safely removing the Little Stars. They also quarantine patients in a building that block its signal from being detected by monsters.

Trivia

 * The Childhood Radiation is a reference to name of Arthur C. Clarke's novel, Childhood's End, which was used by series writer Otsuichi as a reference material. Meanwhile, Carellen Element, the material used to attract Little Star is a tribute to Karellen, an Overlord and the "Supervisor for Earth", the character from said novel.