The Living Saw is a synthesized item in Atelier Meruru: The Apprentice of Arland. It is part of the living tools set. All of the recipes in this set are given to you by Rorona after your alchemy level reaches 20. Meruru will need to make and deliver several of these for development at Cape Ichijo during the Cape Ichijo I development quest. Delivering the saws and lumber needed for the development quest will build the bridge in the area, allowing Meruru to utilize this handy shortcut.