Rewinding to when Yukio learns of Ernst's plan; he threatens to kill him, but learns that a weapon of mass destruction dubbed "the messiah" is to be dropped into the Gehenna Gate, to completely destroy the demon world. Yukio offers to give his blood in Rin's place in an attempt to save his brother's life; however, moment his blood mixes with Rin's, it awakens his demonic powers. The gate begins forming as several of the exorcists are burnt by blue flames. Satan makes contact with Yukio, showing him the past of his mother - Yuri Engin. She was an exorcist who was sent to investigate mysterious spontaneous combustions, only to encounter Satan; immune to his blue flames, she survived his attack, latter searching him out and letting him possess her so he could experience Assiah. After sharing her body for over a year, She ended up pregnant with Rin and Yukio; her own father, Ernst, ordered her burnt at the stake. Satan then inadvertently caused the Blue Night massacre as he searched for a vessel to save her, eventually, he used Ernst as a temporary vessel, to free Yuri, who fled back to the woods and gave birth before passing. Mephisto and Fujimoto were sent to hunt her down and kill her and her children but,after witnessing Yuri's last moments with her children, Shiro was unable to bring himself to kill the twins and adopted them instead, Mephisto decided to help by sealing away Rin's powers and lied to the Vatican. Yukio confronts Ernst, who confirms Satan's story, and inadvertently causes the man to be sucked into the Gehenna Gate. Satan possesses Yukio, realising that since they are family, he can use him as his vessel.