The Masamune is a long, curved blade wielded by the legendary Sephiroth (Final Fantasy VII, Kingdom Hearts 1, Kingdom Hearts 2). Sephiroth uses this tremendous sword to cut things and kill several people throughout the course of events in Final Fantasy VII. The Sephiroth Masamune can be wielded only by Sephiroth, due to it's shear size and weight. It is rather unbalanced, considering it is 40% longer than the average human height. The sword is a great sight to behold, and you best be sure you are on the winning side when it is brought out in combat.
Sephiroth uses this sword, along with the power given to him thanks to Jenova cells infused with Mako energy, to help win battles in Wutai, for example. He is virtually unstoppable in combat, and few people, except Cloud, are insane enough to battle him.