From Grimm wiki
Wesen
Wesen are a diverse group of supernatural creatures living in secret among humans, possessing the ability to shift into animalistic forms known as woge.
Wesen are entities that exist alongside humanity, often hiding their true nature behind a human facade. While most of the population remains unaware of their existence, individuals like Nick Burkhardt, a descendant of the Grimm line, are capable of seeing their true forms. When a Wesen undergoes a transformation, a process referred to as woge, they reveal their distinct supernatural characteristics, which vary greatly between species such as the Blutbad, Hexenbiest, or Eisbiber.
Social Dynamics and Interaction
Many Wesen integrate into society by holding regular jobs and maintaining relationships with humans, as seen with characters like Monroe and Rosalee Calvert. However, their communities are governed by complex traditions, hierarchies, and occasionally dangerous organisations. Interactions between Wesen and humans can be fraught with tension, particularly when criminal activity is involved, often requiring the intervention of allies like Hank Griffin or Sgt. Wu to maintain order.
The Role of the Grimm
Historically, the relationship between Wesen and the Grimm lineage has been defined by conflict and fear. Because Grimms were traditionally tasked with hunting and eliminating dangerous creatures, many Wesen view them as an existential threat. This dynamic has evolved over time, especially through the cooperation between Nick Burkhardt and his Wesen associates, who work together to navigate the threats posed by both the supernatural world and the human legal system.