Rust is a shortsword with an origin that seems to defy most senses of causality, appearing abruptly a few months after the first true counterdemonic inscription was forged, but dating back seemingly longer than that. With its name given due to a normally dark red hue, it crackles to life and becomes an intense cherry red whenever a demonic presence is nearby. This is thought to be a result of whatever magic was put into its creation, as when used in battle, it has been found to be especially lethal to demons, and is thought to be one of the first to be produced with such an enchantment. That, however, is not the most interesting thing about the blade.
The most interesting thing is the presence attached to it.
The first people to find it initially ignored it, only to find that the blade seemed to follow them when the group took their eyes off it, finding it propped up in prominent, but never confrontationally-close positions despite no one ever being close enough to move it within or outside of the group. When a member of the group finally got close enough, he heard a simple greeting in his mind, and a request to be taken to a nearby town. It was under the consultation of a blacksmith and an archmage that everyone had realized that the sword had so many different enchantments put into it, that it had essentially grown its own soul.
The being known as Rust - sharing their name with the sword - is known to be a friendly individual all around, albeit lacking in social skills due to being limited in communication to whoever's close enough to hold it and willing to act as their mouth and a pair of legs. Rust is capable of locomotion through ambiguous means, as they can't move unless they're not being observed, and even they don't know how to describe what they do or how they function. All they do know aside from this, is that they are very claustrophobic due to being unable to see or hear much while inside a scabbard, and request to be either partially wrapped in cloth, or kept in specialized "open ended" scabbards that allow them visual clarity. Fiercely defensive and high in moral fiber, they consider themselves a mentor of sorts, able to guide the hand of the wielder to an extent, and share their radial and spiritual sense with the wielder.