The Sword is a weapon which can be selected for any of your heroes. It is a single-handed weapon which is very good for attacking single opponents.
A sword can only attack one opponent per turn. Also, the range is limited to the first opponent is sight (ie: you cannot attack an opponent behind another opponent: you'll have to attack the opponent in front first).
This gives the sword a limited range. However, it will give a 50% ATK bonus on any strike, making it the best weapon for attacking single, strong opponents.
Ryall also receives an extra bonus when using a sword due to his Innate ability.