Defensive/offensive

A pair of bird-like wings, almost the size of a human

They're made from energy, appearing as a wing shaped thin crystal, filled with a pulsating cloud made of smoke/fire. In the materialized shape, they seem to be normal bird wings, although they are warm to the touch, even after they had been cut off

The wings are surprisingly light for their size, weighing roughly as much as a fake wing, made of thin light wood with feathers glued on it

Gelves start developing wings in their 10th year of life, but can't use them properly until they reach about 150 years of age. Young gelves can't fly but can use their wings to shield or warm themselves. Adult gelves have a pair of thin light marks on their skin in the place where their wings are

Despite being wings, a gelf uses them more as a shield or to launch sharp feathers at their enemies, rather than for flying. They can also work as distractions during battle, slapping the enemy with them. The projectile feathers are thin and seem to be very fragile but are sharper than any blade forged by humans. As shields, they are fire proof and nullify shock, very good for direct attacks.
Humans discovered how to use the wings even after cutting them off, using the blade feathers for weapons, although most pairs of wings are hang up on walls as a trophy. The wings themselves and the weapons made from them are extremely rare and therefore expensive, because of how complicated and long the preserving process of the wings is - without the preserving process, the wings would be reduced to dust in a matter of hours

The feathers from a Gelf's wing can burn and cut through most materials, but with a special treatment, they can be turned into weapons that can harm gelves themselves