Nests

Nests is a term in Heavenly Dragon King's Rebirth to describe special groups of stray devils who band together in order to fulfill a common goal or interest. This could range from protection to even going as far as wanting to destroy or get revenge on the Underworld. Most Nests are made up of stray devils who became stray because of sinister motives, a perfect example of this is the Stein Nest, the first stray devil nest shown in the series was made up of wicked strays who banded together solely for power. It is revealed that stray devils who band together in a nest are always stronger than lone stray devils because they were attracted to each other's power like magnets.

A special group in the Underworld known as Infect was created by the 72 Pillars in order to destroy and bring an end to many of the nests who started to form after the expansion of the evil piece system. Stray Devil Nests are shown to possess a variety of powers and abilities as they grow stronger and gain more power by banding together and experimenting with each other in order to increase their powers to fulfill their goals.

Summary
It is unknown when Nests first began to form, the early accounts of Nests were simply groups of stray devils who banded together for survival or simply to bring harm to the families of their former masters, most fleeing to the deepest parts of the Underworld in order to hide and plan their revenge however as time past, the Bael and many other Noble King families began to notice these Nests were getting stronger and stronger, with some nests even being able to fight on par to High and Ultimate Class Devils and Angels.