In the main story, the Holy Sword was founded by Salesian, who passed the art down for his descendants. Isai however, who is able to use it and is a descendant, has yet to receive the skills of the Holy Sword from Salesian.
Rumours said that those who has perfected the skill of Holy Sword will make any demons tremble before the wielder.
Reinhardt also wields the Holy Sword but instead became a corrupted Holy Sword wielder due to his choice of weapon.
Holy Swords can utilize the Divine Energy of Holy Sword, which accumulates Divine Energy as time passes. When holding down a skill, a Divine Explosion enchance the Holy Skill, making it deal greater dmg or cause special effects. When used, all Divine Energy will be released and re-accumulate. This takes 12 seconds.
This is unaffected by the SPD stat or any other stat. The only way to reduce the cooldown is through the weapon mastery.