History
When the Aesir/Vanir War ended, Siriana of the Aesir and Heimdall of the Vanir, who loved each other but couldn't be together because of the war, finally got their chance to be in unison. To save bridal modesty, a dress was confectioned in order to prevent Heimdall, the All-Seeing, from seeing through it.
However, the wedding never happened, and the dress was left protected in the Union Temple, where All-Father Odin and Freyja married, in Vanaheim. Only those who had no need for it could steal it, while those who had could not.

Angela finds Siri's dress
Properties
The main purpose of this dress was to save Siri's bridal modesty, and thus was confectioned to be the one thing that the all-seeing Heimdall couldn't see through. Due to its magical nature, it will be whatever its holder considers beautiful. For Angela, it became a winged suit of armor. The wings projected by the dress allowed Angela to fly at high speeds in a matter of seconds.[1]