Masa & Mune, known in Japanese version as Grand (グラン Guran?) and Leon (リオン Rion?), are beings of extreme power who appear in both Chrono Trigger and Chrono Cross. In both of the games, they are brothers who are associated with the legendary weapon Masamune. Mune the wise is the younger brother while Masa the brave is the older brother.
Later, when Crono's party seek the Masamune in the Middle Ages, they enter the cave and see the sword. When they go to take it, a human child appears and asks if they want the sword. When the party tells him they do, he calls his big brother Masa who soon appears in the form of a human child, calling them buffoons for thinking they can make a name for themselves and be christened a "Hero" just by claiming the Masamune. He goes on to say that it is how you use a sword that matters, not that you have the strongest one. He asks Mune what they should do, who says that they should test them. They then transform into their real forms and fight the party. When they are defeated, Mune comments that they are tough and Masa says that nobody has lasted this long since Cyrus. They decide to fight them "for real". They say that with Masa's bravery and Mune's brains, they are unstoppable. They then merge together and transform into Masa & Mune.
When the party defeats their combined form, they come apart and return to their original forms. Masa says that it was fun fighting them, and Mune asks his brother if they will fix them and if they will find their proper owner. Masa says that it will be alright, so they go into the sword and allow the party to take the broken Masamune. When they take the sword, Masa says that he will have them ride the wind to the base of the mountain.
When the party arrives in the Antiquity, they see Masa & Mune in Zeal along with their sister, Doreen. When the party goes to prevent the Mammon Machine from being activated, Melchior gives them the Ruby Knife. When they arrive at the Ocean Palace, Mune says that he feels "dark energy" filling the place and that something frightening stirs, disappearing after. As the party progresses through the palace, they see Masa, who says that Dreamstone has been used throughout the ages and that the Mammon Machine, the Pendant and the Ruby Knife were made from it. He goes on to say that he and Mune are the "embodiment of Melchior's hope, sealed within" the Ruby Knife and that hope rests in their hands.
When the party reaches the Mammon Machine, As Crono throws the Ruby Knife into the machine, which later transforms it into the Masamune.
In Frog's sidequest, after he sees Cyrus' ghost, the Masamune comes off him and Masa & Mune appear, saying that his "emotional baggage" was weighing him down and that the Hero's strength is the strength of will. Mune says that he can not save the world if he is dwelling on the past, and Masa says he is truly strong now, and now they can use all of their power. They enter back into the Masamune and Frog takes it back, commenting that it is now in its true form.
Masa & Mune
When the players fight Lavos, it will have the same strength as the bosses you've faced in the past. One of them is Masa & Mune.
In Chrono Cross, the brothers return as avatars of the Masamune. Though less central to the game's storyline, the Masamune remains a powerful, though corrupt, weapon. After defeating Dario during a sidequest, Masa and Mune would appear and reveal that the evil power which corrupts the weapon was allowed to enter because they were sleeping. Their big sister Doreen appears after chastising the boys for allowing this to happen, she fuses herself into the blade, along with her brothers. with Serge's original weapon, the Sea Swallow. This creates the Mastermune, the most powerful weapon in the game. In the Japanese version, it's known as the "Guran Doreen" and is a play on words meaning "Grand Dream".