The Sword of Michael, or the Flaming Sword of Michael, is a mighty and tremendously powerful blade that is used by the archangel Michael. The sword was given to Michael by God himself in order to combat his brother Lucifer alongside his rebellious army of angels. Being the eldest and most powerful angel in creation, it makes sense why Michael would be entrusted with such a blade. It is called the Flaming Sword of Michael due to the fact that it, obviously, uses a form of powerful holy flames that are capable of extinguishing unholy beings of darkness into ashes, or even nothingness completely.
When released, the blade is engulfed in fire. The aura of this weapon disintegrates everything and anything which Michael waves the sword at, changing it into nothing more than ash, and engulfs the surrounding landscape in a blazing firestorm, the heat of which is intense enough to even scorch the sky. Only powerful archangels such as Gabriel, Raphael, Uriel, and Metatron can resist it, but even then only indirectly. Lucifer was able to resist the intense flames of the sword when facing Michael head on due to his power rivaling the great archangel himself.
Michael is also in sync with his blade, and thereby allowing him to have complete control of the flames themselves. He is capable of contorting and twisting the shape of the flames themselves, for example allowing them to take the shape of a large Griffon or other animal, and when he releases a wave of flames, he can even control the direction of where the flames are being thrown at.
Michael's sword can only be wielded by those who have a righteous heart and a powerful force of will. When humans lift it, they are either unable to, or even if they do it acts like a normal sword. When a demon or other creature of the darkness attempt to lift it, they are immediately incinerated upon touching the handle alone.