There are three unlockable bonus weapons in Dynasty Warriors 7 for the PS3 and Xbox 360.
Here are the unlockable weapons, and what you need to do to unlock them.
Spear
Silver Stallion – Unlock all cities in Conquest Mode
Sword
Quilin Blade – Complete all stages in Conquest Mode
Twin Swords
Silver Swallow – Get 100% in the Scholar Quizzes