I found this on a webpage just about him!

"Yousui is one of the Demon Kings of Tenkou, a
being bent on ruling both the world of the book
and the real world. Yousui is the last of the
Demon Kings, but he is also definitely one of the
most dangerous out there. With the ability to use
sharp metal wires that can even wrap around
spirits, Yousui is already a formidable opponent,
but he also has the ability to take on other forms
as well using parts of them as mediums.

Yousui is able to take the form of Tamahome in
order to confuse the Suzaku Seven and especially
Miaka, who had been searching for Tamahome's
memories in order to help the real Tamahome (now
called Taka) regain his true ability. Totally
fooled by Yousui's appearance as Tamahome, Miaka
nearly gives in to the Demon King, but her love
for Taka seems to conflict with her old feelings
for Tamahome. For Taka's part, he begins having
feelings of worthlessness next to Tamahome, and it
takes motivation by Keisuke and the others to
convince him to fight for Miaka once again, to
defeat Yousui in his new form."

Now didn't ya just want to know THAT much?? ~_^