Kuchikake Ryuu no Keiyakusha

Yao is a 16-year-old boy who inherited an antique shop left by his grandmother. He also worked as an exorcist, exorcising evil "koware," which are antiques that have been treated with care for many years and have come to possess souls, but whose hearts have been tainted by darkness and attacked people for various reasons. In the past, he was attacked by an antique that contained a "fearsome spirit," which put his sister Meilin in a coma and kept her age at 12. Ever since then, he has been pursuing the koware that attacked her, determined to find the clue that will awaken his sister. But then he was attacked by a koware and nearly died. Yao felt despair, wondering if he would die without accomplishing his goal, when he was rescued by a giant dragon with ancient power!

What is the true nature of this dragon? And where will their encounter lead...?

(Source: Akita Shoten, translated)