Sesshoseki

The Sesshoseki is more conceptual, than physical as a weapon. It appears as a swirling mass of silver flames like an orb of Amaterasu flames, although on its own, barely poses a threat to any competent shinobi. Wielded by Avalon Lucetius's Susanoo, one of its two divine tools, has its true power realized when Avalon determines which weapon will play host to the orb, be it one of his own weapons or a plain Susanoo Sword. Be as simple as that may sound, the metamorphosis staged immediately after is nothing short of mundane.

The orb adopts the form of the selected weapon, increasing its size to scale of a regular, Susanoo-wielded sword (if it weren't already one) and granting it ethereal properties. This combined with the application of senjutsu chakra, which can easily be insulated throughout Susanoo's framework dramatically amplifies the capabilities of the host. The weapon is also shrouded in a silver chakra-hue, which negates jutsu it makes contact with merely by slicing through, or contaminating the chakra composing it.

Were Avalon to select an average Susanoo sword, its size would double, as would its strength and overall lethality. It would easily cleave through another (average) Susanoo sword and unarmored Susanoo.

Were Avalon to select his Nanatsusaya no Tachi, it would instantly enter its transformed state, being transfused with an excess in senjutsu chakra (were Avalon in sage mode when activating Susanoo), and gain an increase in size equivalent to that of a Susanoo sword. It would retain all of its abilities, while empowering those which can be, even in the slightest.

Influence
The Sessho-seki (Japanese: 殺生石), or "Killing Stone," is an object in Japanese mythology. It is said that the stone kills anyone who comes into contact with it. The stone is believed to be the transformed corpse of Tamamo no Mae, a beautiful woman who was exposed to be a kind nine-tailed fox working for an evil daimyo plotting to kill the Japanese Emperor Konoe and take his throne. As told in the Otogizoshi, when the nine-tailed fox was killed by the famous warrior Miura-nosuke, its body became the Sessho-seki. The Sessho-seki was said to be haunted by Hoji, the transformed spirit of the kind fox, until a Buddhist priest called Genno stopped for a rest near the stone, and was threatened by Hoji. Genno performed certain spiritual rituals, and begged the spirit to consider her spiritual salvation, until finally Hoji relented and swore to never haunt the stone again.