Black Plague

In GE2, red rain is a pandemic spreader of an incurable disease called the Black Plague. When one makes contact with the red rain or afflicted patients, he/she will be inflicted with the plague. The Black Plague spreads throughout an infected body by indication of black-reddish marks being left visible on skin. Once the plague marking has reached a certain point, the infected will die. Other symptom is chronic coughing. Several child inhabitants of Anagura are infected wtih the Black Plague. There has been no cure for this plague and death is 100% guranteed for infected patients. Aragami do not seem to be affected by the red rain.

History
Between the two year interval of the events of God Eater Burst and God Eater 2, red rain mysteriously started raining over the far east region spreading a 100% death-causing pandemic to those who touched it. No cure is is avalable for the increasing pandemic. With the appearance of red rain, God Eaters are unable to enter the field without contracting the plague which leads to the further development of God Arc Soldiers, mechanical soldiers that can be ridden or controlled to fight Aragami even in red rain.

The Red Rain and Black Plague are actually part of a system to find+make a new Singularity after the prievious one (Shio) had left to the moon. Infected patients are victims of this search/creation for the new singularity and are fated for death if the plague progresses enough. Two of the qualifiable candidates of the new Singularity are Julius Visconti and Yuno Ashihara. The Person Who Opens the World is the transformed Singularity state of Julius when infected. After Blood defeats him, Julius uses his Singularity power to extract the Black Plague off from infected people which returns them to normal. No more red rain has fallen ever since then.

Additional Information

 * The Red Rain and Black Plague first make their appearance in the prologue manga,God Eater: the 2nd break, which crosses into the GE2 plot and also depicts events that occured before the game.
 * Coincidently, the markings found on Shio's body and on plague-infected patients seem similar in design.