Hrunting

The demonic sword Hrunting, the Hound of the Red Plains (赤原猟犬), is a Noble Phantasm used as a Broken Phantasm by Archer in Fate/hollow ataraxia, during the 4-day loop reenactment of the Heaven's Feel 3.

It is a pitch black weapon, with a few small edges coiling around the thin core, spiralling around it and somewhat curving outward. It seems to be hard to pull out once it has struck.

Archer used it as an arrow to shoot at the broad bridge in the middle of Fuyuki city, standing from the top of the center building. The distance between these two places is approximately 4 kms, and the arrow was shot at mach 13.9.

Its usage as a sword is unknown, but when shot like a bullet or as an arrow, it turns into a magical bullet envelopped in a red light, and it will keep tracking its target once it is shot as long as the shooter keeps aiming at it. However, it hasn't been verified if it could have done a 180° change of course to pursuit Saber when they passed each other.

Similarly, after Archer shot it while targetting Emiya Shirou, it is unsure if he would or not have been allowed to switch target to Saber when she simultaneously jumped from the bridge in an ambush attack. It might be an unconditional attribute of the weapon, or a choice from Archer, or a little of both.

Furthermore, when Saber was repelling it from the ground, it was taking around 30 seconds to charge it with prana. When Archer fully charged it (around 40 seconds?), it took one second to reach its target even with the strong wind that was swaying the handrail of the bridge.

Source: based on the Tsukihime Laboratory entry and the dictionary resource at Jonnobi.