Both Shana and Kazumi stand at their respective locations waiting for Yūji to meet with one of them, only to discover that Yūji has disappeared, with not even the slightest evidence of his existence left behind. All is not lost however, as the letters the two of them sent to him still give hope of Yūji's continued existence. As Shana and company search for answers on Yūji's whereabouts, they soon find the truth staring back at them when Yūji reappears in front of them as the leader of Bal Masqué. Left with little choice, Shana must now confront her most unlikely adversary on the battlefield in her most difficult challenge yet.

Shana and Alastor — the Lord of the Crimson Realm — continue to do battle with the Guze no Tomogaras, who are trying to steal the Power of Existence from mortals. In the last battle, Yūji is revealed to be a mystes, a torch with nearly unlimited Power of Existence. Since the Tomogaras want to capture Yūji and use him to upset the balance of the Realm, Shana resolves to protect Yūji. Yūji then vows to join Shana in her fight.

The 15-year-old Sakai Yūji used to be a normal student, but one day that normal life ended, when he was assaulted by a monster, Guze no Tomogara, from another world that turns humans into edible light. Luckily Yūji was saved by Enpatsu Shakugan no Uchite, a girl with burning hair and red eyes. Though when she tells him, "You don't exist any more.", Yūji knows that his normal life has ended...

Season 0 of House of the Dragon premiered on January 25, 2006.