Kimon

Kimon (鬼化, Kimon) is a mark of a demon that holds a Shou's negative feelings mostly hatred. They're stronger than a onigami that just simply transform Hayagami into aggrandized demon along with it's Shou.

Origins & Uses
The origins of the Kimon are particularly unknown of regular obtain, but it derived alternatively from the Hayagami Orochi; that uses dark abilities in a rare case.

For those who had the Kimon mark are able to transform into into a formidable beast. Hayagami will absorb into them and unleash the Kamui from their body and became even more powerful. The first stage of their demon form is that their humanoid fighting form completely changes to become more powerful. The second stage of the demon transformation is that they change into a complete beast altogether fully merging the Hayagami into them.

Demonization
List of Shou that have the Kimon mark and the transformation of a demon: