It has the form of a katana.
Fidelacchius, also called The Sword of Faith, is one of the three Holy Swords made from the three nails of Christ’s crucifixion. It has a scabbard that makes it look like a cane.
It glows when in combat, and is a very powerful object of faith. When used incorrectly, the enchantments will break.
It was formerly wielded by Shiro Yoshimo, and was given to Harry for safe-keeping until the next knight could be found, until Changes. It’s now with Karrin Murphy, who seems to be a strong candidate for the next bearer.
Like the other two swords, it’s powers become vulnerable when the wielder succumbs to the opposite principles the sword holds. In this case, the sword becomes vulnerable when the wielder breaks a promise.
In Ghost Story It’s revealed by Sir Staurt, that the blade is actually the legendary Japanese sword Kusanagi, it’s name is translated as “The Grass Cutting Sword” or “The Sword of Gathering Clouds”. In Japanese mythology the sword was said to have been forged by one of the three main deities, Susano’o the god of storms, and given to the Emperor of Japan, the descendent of Amaterasu, the god of the sun and light and another one of the three main deities. According to the Imperial family they still have the blade, but no, you can’t see it…
It was wielded by Shiro Yoshimo. After his death it was used once by Karrin Murphy.