Yuria the Witch is a character in Demon's Souls.
Yuria is located in (1-3). To save her, the player will have to complete most of 1-3 to get a key, backtrack to 1-2 to obtain another key, and finally disguise yourself as a Fat Official by using the Official's Cap to gain access to the area she is in. After you rescue her, she will be in the Nexus.
She teaches you advanced dark magic by using Demon's Souls. See the Magic/Miracles section for a list.