斬 means "beheading"
Namakura is one of the more "normal" blades in that it's based off a regular katana. The handle is adorned with triangles, with the handle having them connect from top to bottom like a chain with a black sheath.
Namakura is known as the sharpest blade of the twelve. Despite seeming rather average compared to the others, it's blade is sharp enough to cut through any object and can be drawn from the sheath at nearly seconds. This drawing speed can be increased by coating Namakura in blood.
Ironically, while being holding the title of the Beheading Sword, Zantō, Kiki Shikizaki named it Namakura, which means Blunt.