The Runeblade is your Heroine's life blood. As she progresses through the game, she will gain Runes on her Runeblade. These Runes will in turn grant her access to Spells. Along her journey she will also find the Rozh Gemstone and add that to her Runeblade. As you can see, this is the focal point of your Heroine's game play. They probably should have incorporated it into the game name somehow...
A Runeblade is the result of centuries of studies and experimentation of the Runic Magic of the Arai. A capable War Mage can instill powerful Runes into a Runeblade through a ritual spell called the Awakening. A Runeblade is a personal weapon, therefore each War Mage must Awaken the Runes in their own blades.