Cilsius Steel (pronounced "Shil-soos") is a type of alchemical alloy produced in the Sakura Taisen franchise universe. It is highly resistant to attacks by evil magic or demonic energy. At the same time, it also happens to be a good conduit for Spiritual and Psychic Power, making it a very useful material for the construction of anti-demon weapons and armor.
All Spirit Armor units, such as the Koubu, are constructed from Cilsius Steel , though the machines themselves also include more mundane elements, such as ceramic plating to defend against normal weapons. Some important landmarks are sometimes constructed (or reconstructed) using Cilsius Steel to prevent them from being destroyed by demons.
In practice, it is essentially Sakura Taisen's version of Adamatium or Mythril metal.
Cilsius Steel (or variants thereof) has existed for thousands of years, often used in the construction of special swords
and melee weapons
to be wielded by demon-fighting warriors. Sakura Shinguji's Spirit Sword
was forged using time-honored Shinguji-clan methods.
The formula and the methods for its production, however, were lost with the rise of the industrial age. Cilsius Steel was only rediscovered during the American Civil War
Over the course of the war, the Confederacy
had begun to gain the upper hand, inflicting heavy losses among Union
troops through the use of Voodoo
black magic. While this is difficult to believe considering Confederate attitudes towards the primarily African-American
practitioners of Voodoo, this is apparently how it happened, so one should just take it at that.
Cilsius steel was discovered by a group of Union troops who had somehow miraculously survived a Confederate magical barrage by taking cover near some old steam tractors
. The tractors and the materials they were made of were sent to Union leadership, where they used in the construction of special armor barricades, bullets
and cannon. The new, highly effective weapons were used to stop and eventually repel the Confederate advance, eventually turning the tide of the war.
Information about Cilsius Steel slowly disseminated throughout the world, but the need for it was not seen until after the devastation of Tokyo, Japan
during the Kouma War of 1918. From then, Cilsius Steel was incorporated into the structure of many important buildings, as well as being used in the development of the new, anti-demon Spirit Armor suits.