Hollow Regalia, Vol. 2 (light novel)

Yahiro Narusawa once lived alone in the ruins of Tokyo, but things have changed for him in the blink of an eye. Now his job is to protect a dragon medium—a girl named Iroha who wields the power of fire and the ability to summon a dragon. Yahiro’s sister, Sui, is also a dragon medium and responsible for the cataclysm that destroyed Japan.
He’s been searching for her all this time, and he’s finally discovered that she’s allied with the shadowy organization Ganzheit. Determined to kill Sui for what she’s done, Yahiro agrees to work with arms dealer Galerie Berith to eliminate both her and the dragons. That said, Yahiro won’t have any trouble finding them, because the dragon mediums and their Lazaruses are coming for him!