Kibisis

is the sack used by Perseus to defeat the Gorgon Medusa and hold the demon's head after it was severed with Harpe. It is an anti-sealing Noble Phantasm that distorts the concept of the world through a mirror world-type Bounded Field that places the inside of the pouch on the outside and the outside of the pouch in the inside. It inflated and swallowed Perseus, creating a fold in space that placed the outside world into the inside of the bag, and Breaker Gorgon, which affects only what is inside, was reflected back, making Medusa look upon herself as if reflected in a mirror, allowing him to slay her with Harpe while she was immobilized.Fate/hollow ataraxia - 10/08 - Emiya's - Mirror of Kibisis
As per legend, it contains the Gorgon's head that has been turned into Perseus's Noble Phantasm.Fate/Grand Order material IV - Gorgon, p.352-363, translated by castor212 at Beast's Lair.
==References==
Category:Noble Phantasms
Category:Unknown rank Noble Phantasms
Category:Unclassified Noble Phantasms
Category:Bounded Fields
Category:Noble Phantasms introduced in Fate/hollow ataraxia
Category:Noble Phantasms of Perseus
Category:Noble Phantasms in Unlimited Blade Works