Yuria was first introduced during the Olympia Arc. Contrary to many English translations Yuria is not Kaito sister as this is a common mistranslation. She is Kaito childhood friend or more likely lovers. She was the container of Lucifuge - the No. 3i Demon until recently when Kaito used the power of his overwhelming love for her to subdue the demon and remove it from her body.
Vova
