As Crono and his party enter the Denadoro Mountains in search of the Masamune, they eventually find the chamber that houses the sword. But in order to get the sword, they must defeat the magical creatures Masa and Mune.
After the battle, Masa and Mune agree that Crono and his friends just might be powerful enough to wield the sword. So they hand it over to them, but it's only the blade of the sword. The hilt is missing.
Masa and Mune magically transport the party to the base of the mountain.
Much later, when Crono's party arrives at Zeal Palace, both Masa and Mune are there.
Masa makes a brief appearance in the Ocean Palace.