My Black Dragon Master

The most powerful dragon tamer in the empire, Kane, captured the black dragon Knox and personally put a servitude collar on him. However, the next night, the black dragon transformed into a human form and fastened the collar around Kane's neck. Every time the double rings were activated, Kane gradually turned into a dragon, while Knox became more and more human-like. When Kane realized that this encounter was from the very beginning a deception, the two had to make a choice.