The characters for Yakumo literally mean "eight clouds" (but can also mean "countless clouds"), and Yukari "violet."

Yukari is an elder yōkai who dwells on the border of Gensoukyou, and may predate the existence of the realm itself. A good friend of Yuyuko's and an acquaintance of Reimu's. She is the self-appointed stewardess of the seal between Gensokyo and the outside world, but doesn't do a particularly good job of it...

Most of the time, she is asleep, leaving all the work to her shikigami Ran and Ran's shikigami Chen. When she isn't, she tends to amuse herself by pulling in unprepared humans from the outside world and stranding them in Gensoukyou. A very irresponsible yōkai.

Her ability is the manipulation of boundaries, and such boundaries distinguish her spellcards. Often, though, she just summons her shikigami and various others to create her danmaku for her.

(Source: Wikipedia)