Elemental Vision

Your genasi is able to sense creatures around it with elemental aid due to their familiarity with their respective element.

Fire: You can see a creature's heat signature. 

Water: You can sense the water in a creature's body, or you could say that it's their blood you can sense.

Earth: You can see through the vibrations in the earth, including ones made by your own footsteps.

Air: You can sense vibrations through the air, essentially using echolocation to see the world around you. 

Each element also gives a special ability for your perception based on which one you choose.