The Double-Beat Rune (not to be confused with the Double-Strike Rune) is quite a helpful friend, as it letting you attack twice in a row without any painful drawback. The actual physical attack will be executed twice, so even mutiple attacks (for instance done by Riou some times) result in duplicated multiple attacks. Due to the doubled attack, the only downside is the double damage received, every time an enemy counterattacks you. That is, considering the advantage given by the rune, a small price to pay.
The Double-Beat Rune is unique in the Gate Rune War, yet not fixed to Eikei's right hand. Most players tend to overlook the fact that you can easily remove the rune and attach it to someone you see better use for it. Three years later more of these crystals appeared, during the fall of the Highland Kingdom, which could be put once again to a good use. Nevertheless there was no trace of a Double-Beat Rune in any other country until now. - Celes