The corrosion of Void power alone would take a long time to transform an individual of the material world into one of the Void camp. Moreover, the more powerful the individual, the longer the time required.
For an Archangel like Auriel, even though she was immersed in this Void, Roy wasn't sure how long it would take for the corrosion to complete, so this was just a casual move. After leaving the place where Auriel was, he wandered in this Void.
In the pair of mist wings behind him, some strange-looking patterns were constantly flickering like breathing lights. After he set the Void Flight ability for himself, they automatically appeared on his mist wings. These patterns seemed to have formed by the system on their own, and they could perhaps be called 'Void Runes'. When these rune patterns shone, he could move freely in the Void.