Cool idea; a broken sword or even handle that can proceed in one of two ideas
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Broken sword that has a technique converts to overpowered sword when fully completed or reforged, granting sick powers
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Same thing, but depending on certain materials you combine the broken one with, could turn into different weapons. You could use the broken sword to make a glaive, great sword, or katana of some kimd.
Inspo: biome blade, and other stuff and meliodas' sword