Ah, I support the theory of a Daniel Krispin. Masa, Mune and Doreen ARE the sword. The Masamune doesn't really take the form of a sword, it doesn't REALLY have a constant physical form. Rather, it takes the form of what the weidler wishes. If Cyrus wanted a kickass sword, it will become a kickass sword. If Serge wanted a weapon that will help him vanquish his foes, which he could weild, obviously, it would turn into a powerful Swallow.
When Masa and Mune form the sword, it is powerful. We all saw how strong it got after Glenn cured of guilt. But once we add Doreen to the formula we have one of THE strongest weapon in the Chrono World. Doreen means passion and dreams, and once you add it with Serge's passion to be allowed to be born into the world and eventually save Schala, you get a pretty powerful weapon.
The point is the Masamune consists of the weilder's power, wisdom and emotion. Doreen fell asleep, perhaps the fall of Zeal was such a shock to her (She is the emotional one) she went into a sort of coma. Once Serge cleansed the Masamune of malice, she woke up. Perhaps the guilt of all the evil they had done had been a greater shock, making her wish to guide her younger brethern?