Suzanna Julia von Wincott (フォンウィンコット卿スザナ・ジュリア) was a member of the von Wincott family. She was engaged to Adalbert von Grantz and was good friends with Conrad Weller. It's stated that she was one of the Three Great Witches; along with Lady Celi and Anissina. She was known as "Julia the White".
Julia was blind since birth and wore a necklace that had a blue stone attached to it, inside the stone was the Wincott family crest. She was very close to Conrad, and she gave him her pendant, which Conrad then gave to Yuuri.
Julia truly believed that humans and the Mazoku could live together in peace. She was kind, and even would give up her own happiness for the sake of others. Her father remarked that she, like her ancestors, had inherited the trait of being mischievous, but she often sacrificed herself for other people. She was a tomboy who was a top class martial artist. Julia was also incredibly skilled at medical magic. During the war, she wanted to help so many people she over spent her magic. Many around her, such as Gisela and Celi, have commented that Julia pushed herself over the limit when trying to help people on the battlefield, which eventually resulted in her death. Gisela was the one who remained by Julia's side during her final moments.
Julia's soul was given to Yuuri when she accepted the fate given to her by Shinou. She was betrothed to Adalbert, and was incredibly skilled at medical maryoku. She appears to have the same views on humans and Mazoku as Yuuri does, wanting both races to be at peace with each other, which signifies their similarities. Julia's blood was the key to the box Mirror's Depth and so Yuuri inherited the key from her because the key is embedded in the person's soul.
In the anime, she was Wolfram's teacher. She met her future self, Yuuri, just before the Luttenberg Division left for the battlefield. Her chance meeting with Yuuri prodded her that she is making the right choice accepting her fate to be the soul of the next Maou and that Yuuri will heal the world in the future.