Growth is a part of the Balance Aspect of the Blood Fysa. All ptheran start with this fysa.
This is an active fysa. Users can shape-shift to grow and un-grow certain body parts:
For ptheran, this means their wings, their claws, and their bone spurs, if they have any. For their wings, their secondary forearms transform into large wings for flight. There is no pain associated with this transformation and the process consumes magical energy.
This transformation comes very naturally. An anxious or on-edge ptheran may display partially transformed wings/claws/spurs as an involuntary flight-or-fight response but, like holding one’s breath, any ptheran is capable of controlling their transformations with acute awareness.