Why does Mikoto's Sword of Damocles break every time he uses it? Why does Mikoto's Sword of Damocles break every time he uses it?
The Sword of Damocles is the direct manifestation of the Kings' powers and their state as a King. If they were to lose control of their powers due to personal emotions like Mikoto's rage of Tatara's death, the swords start crumbling. This is due to his Weismann levels raising as his compatibility as the Red King is falling. A similar thing is happening to Reisi Munakata, where due to him killing Mikoto, that burden of killing a king is causing his sword to start crumbling as well.