Gáe Dearg

This is the long spear that renders useless any magical defense. Any protection made of prana will be rendered ineffective, and any weapon magically enhanced struck by Gáe Dearg will be rendered useless. In effect, this is a perfect "anti-Noble Phantasm" spear that can be defended only by physical means. Still, a contract or curse already completed cannot be cancelled.

The 2 meter long red spear is normally wrapped in a talisman cloth. This demonic spear was passed to Diarmuid by his father, the druid Angus.

The "dearg" in the name means red.

Sources: Fate/Zero vol. 3 status page and the dictionary resource at Jonnobi.