Mark landed on the school roof with Dona in princess carry, and his wings contracted behind him. He kept a note of his surroundings with his Soul Sense.
Sometimes, a person can feel when someone is looking at you from the back. The Soul Sense was a way more potent version of this 6th sense.
It was not as clear to visualize things it saw as it was to visualize with your eyes. It was not as audible in terms of noise when compared to his ears, and it was not nearly as good as the skin in terms of understanding texture and temperature.
But the Soul Sense was somewhat very special. It was more of a complimentary sense to all of his other senses. It couldn't move into walls or see through opaque objects like he would have liked, but it could enter through holes and see things.
His current Soul Sense could stretch as far as 92 meters from him.