Ancient Blades are a material found in Tears of the Kingdom.
Tears of the Kingdom
"An ancient dagger-like blade. It's too small to wield as a weapon, but it can be used as an arrowhead."
The Ancient Blade can be fused to an arrowhead while drawing the bow. It has a fuse attack power of 50 and functions as an Ancient Arrow when fused with an arrow, disintegrating enemies in one hit just like in Breath of the Wild.