When practitioners of Shugendō went up into the mountains, axes like this one were used to cut the branches and clear the brush in their path. Originally, these were used as a tool, but they came to take on a ceremonial function as a ritual implement. The blade of this axe is made of iron, and it is shaped like a plectrum for strumming stringed instruments. There are heart-shaped openwork designs decoratively bordered with bronze. The handle is made of wood wrapped in a bronze sheet.
 
NAITO SakaeEnglish by Mary Lewine 
Buddhist Art Paradise: Jewels of the Nara National Museum. Nara National Museum, 2021.7, p.338, no.144. 

A ritual ax is a symbol of virtue, which was supposed to cut off the worldly temptations of Buddhist monks who were under training on mountains. Usually, the monk who walks at the head of the party is holding a ritual ax. These ritual axes are called "Nyūbu-no-ono" (mountaineering ax) as monks used to have real axes to make way when they join the training on the mountains.
This rather thin ax is made of forged iron. The cutting edge of the blade is curved whereas the head of the blade is made in the shape of a flower. There are two heart-shaped open-work decorations; the hearts are rimmed. The handle is made of wood, and both ends of the handle are covered with gilt bronze plates with heart-shaped decorations rendered in open-work. A thin gilt bronze belt is coiling around the handle stick from one end to the other. Judging from the manufacturing technique, this ax should have been made sometime between the Nanboku-chō and Muromachi periods. This ax, as well as a similar ax kept in the Yamato Bunka-kan Museum, is an excellent work of art. Although it is a ritual implement, it has several characteristics of a tool for practical use. A ritual tool with practical characteristics indeed fits to the mountaineering priests. This ax had been kept in Jinshō-ji temple in Shiga prefecture. 
Masterpieces of Nara National Museum. Nara National Museum, 1993, p.126, no.100.