Regarding the sword of light in a serious manner...
Kenikari - Sword Light - Sword of Lights
This blade is believed to have been forged by the Seraph, containing a powerful magic and a soul sealed within it. The blade is often mistakenly called the "Sword of Light" because of bad translators, but in reality it contains many lights, and uses many different types of magic. The magic is typically fire, light, and wind styled magic; using these magics of the void the sword can easily slice through the veil between this world and the Void. It has vanished into history along with the Seraph civilization, but is rumored to lie somewhere in the heart of Old Ceardia, and is said to have been the cause of the Doom - someone created a gateway using its power and through it game the destruction and demons of the Void, just as they had come through the original gateway and layed waste to the Seraph.
Alternate:
The "Sword of Light" is not an actual sword, but a type of magic that allows access to the source of magic, the Void. Designed to cut through the veil between Aloria and the Void, it was crafted by the Seraph in a misguided attempt at gaining more magical energies. Called the "Sword of Light" it is in reality a sword forged by mixing all the known types of magic into a single powerful spell. The appearance of this spell is a deep black emptiness filled with stars, with the original Seraph name being "Gate of Candles" which was eventually turned into "Sword of Light" as time passed. The "Sword of Light" allowed the first demon invasion that toppled the Seraph, and when SilverEdge created their own attempt at a "Sword of Light" to gain more magical power so that they could battle the Dark Banshee it unleashed the Doom of Ceardia. As of now, the status of the "Sword of Light" in SilverEdge is unknown, but it is assumed to still be functional because the Doom remains.