Board Thread:Theories Discussion/@comment-6946747-20130306192825/@comment-6192846-20130307004619

Well, a sin seems to gain its power based on each "epitome" of that sin being commited. This makes sense since demons usually "feed" off the vices and negativity of humans for various reasons such as sustenance, pleasure, or to gain power; the demons possessing the vessels of sin seem to be in the latter category.

Likely the anger fueling Kachess was not enough for the sin to "break" whatever barrier it needed to overcome in order to reach its full potential and awaken, which seems to be the ultimate goal of all the vessels of sin.

Clarith was supposed to commit the epitome of sin out of her hate and anger at Riliane for ruining her life (which she did) but was stopped by Allen. The destined sinner of Wrath failed to accomplish what she was fated to due and the burden was carried over to [Insert name of Wrath sinner portrayed by GUMI].

The key seems to shapeshift by the will of the wielder but until details come out from the Venomania novel on how Kachess acquires it and knows how to use it to kill Venomania, we cannot say.