The Onmyoujis:
Long before the Shogunate established, Onmyoujis has been the protectors between the living world and the under world. Onmyoujis are also civil servant positions which observe the stars, keep track of calendar, as well as fortune telling and evil dispelling. They were said to be able to make use of the power of the five elements: metal, woods, water, fire, and land. Also some of them had “Shikamis” serving them, who were life force extract from nature, enslaved minor demons or raised from dead beings.
Byaku's family, namely “White”, or “Weiss" in German, was one of the Onmyouji house expert in hand to hand combat against Youkais, monstrous beings and evil spirits. They enhance their power with the five elements while having powerful yet replaceable, relatively expendable shikamis fighting at their side against tougher enemies.
They were also the keeper of the “Yatagarasu”.
Weiss’s clothing:
Based on Junihitoe, namely “12 layers” in Japanese, is a traditional style trended among noble house members in ancient Japan, which you wear 12 layers of fancy clothing on you, weighting 20 KG. It is, of course, impractical wearing that to combat, so the one on her was simplified to 6. The colors, accordingly from outside to inside, were white, gold, brown, light blue, yellow, and red, representing the five elements and the color of her house.