The Buster Sword, the legendary blade from the Final Fantasy VII world, is an enormous weapon that was first seen in the hands of Cloud Strife, the protagonist of Final Fantasy VII.
The origin of the blade, however, was with the SOLDIER 1st class named Angeal Hewley, who was the mentor of Zack Fair in Crisis Core: Final Fantasy VII. The sword was given to Angeal by his father, and it stood as a symbol of honor and pride to the 1st class, and he did not use it unless it was absolutely necessary.
When Angeal discovers his origins through the Project G, he thinks himself to be a monster, and uses his horrific newfound power to assimilate others into his own body. He then forces Zack , his once favored student, to fight and kill him, and free him from his monstrous life. In his final moments, Angeal passes the Buster Sword to Zack, and instructs him to never lose his SOLDIER honor.
Zack then carries the sword against Genesis Rhapsodos, the antagonist of Crisis Core, who was also at the center of Project G. Zack is able to defeat him, but his victory does not save him in the end. He and Cloud , who at this time was a Shinra Soldier, are captured by the mad scientist Hojo, and experimented on at length.
Zack manages to escape, dragging the comatose Cloud away from the lab, and attempts to return to his love, Aerith, in the city of Midgar. The journey is cut short by an enormous mod of Shinra soldiers, who kill Zack , who in his extremely weakened state, hides Cloud from them. The dying Zack then passes the Buster Sword to Cloud in a similar manner that Angeal had given it to him.
Cloud then uses the weapon in Final Fantasy VII to hunt and defeat his sworn enemy Sephiroth, all the while struggling with his identity, and the fact that the experiments that were used on him caused him to mistake Zack 's past for his own.