Remnant Beasts usually build nests only in safe environments.
To collect enough materials and provide sufficient magic power, most Remnant Beasts will pick a relatively hidden, food-abundant place to start building their nest.
This is also the main basis for many Magical Girls when they hunt pupa-level Remnant Beasts. They use this as a standard to locate potential nesting sites, waiting at these sites to eliminate those pupa that haven't had time to build nests and cannot fully utilize their powers.
However, there are always exceptions to everything.
When too many pupa-level Remnant Beasts fail to build nests in time and are hunted, and when too many pupa leave their nests only to be eliminated by Magical Girls or other Remnant Beasts, the natural law of survival of the fittest comes into play. Those that survive and grow successfully usually possess some extraordinary abilities.
