Masks () differ between Vespers and Angels. They materialize in front of the user's face, and disintegrate when not in use. Shattering a mask is a mark of defeat. They serves as a disguise, a shield, and personification of their power.
For an angel in human form, the materialization of a "mask" is the first step toward becoming their true form. They increase in power levels, with their spiritual density exceeding that of most people around them. The density of spiritual matter at this stage can be great enough to impact the physical world around them.
Vespers materialize a mask when accessing the power granted to them by their angelic host. For many Vespers, this means borrowing from the power lent to them by Vouriot. Their power level is increased tenfold, but at the risk of the Vesper's own wellbeing and their environment. Most Vespers only pull out their masks when within a pentagram, or other perimeter that can limit their influence over the local environment.
The use of the mask comes with a price, however. After using such a great amount of power, many Vespers become weak directly after a battle; consequently they easily fall prey to hunger or the desires of their host. Thus their vampiric tendencies are strongest right after the loss of the mask. They are the most vulnerable to possession (by their host or by other spirits) when exhausted by use of their mask. Sometimes this happens during use of their mask as well, such as when Hanata Hibari attempts to rescue Fuyuki or .