Talk:Kokushibo/@comment-39227821-20191106221523/@comment-44081368-20191218013829

Red swords stop demons from regenerating. When a demon slayer gains the mark, their body has to be at a high temperature, therefore heating the blade and causing it to turn red like in those 1000 degree knife videos. Though we have seen demon slayers heat the blade in different ways, Nezuko's fire, striking two blades against each other. The red represents the blade becoming hot and the intense heat stops demons from regenerating for a while.