At least 1,500 years ago, a gifted swordsmith forged the katana that was solely used for Shinto rituals as a ceremonial sword. At some point, Fukuchi later possessed the sword and utilized it for combat, contributing to garner him countless victories throughout history against various sorts of opponents, which eventually led to his renown in his military career as the legendary samurai war hero.
Amenogozen is a blue-bladed katana with a tsuka-ito wrapped around its handle and a radial-patterned tsuba, an appearance of which was described by Atsushi Nakajima as "beautiful". Fukuchi can also summon it out of thin air whenever necessary. As with other swords, Amenogozen is made of metal.
Befitting its nickname as the space–time sword, Amenogozen can slice through airspace with a limit of at least a dozen centimeters, but Fukuchi enhances its reach with Mirror Lion, which allows him to penetrate farther than its spacial range. The sword can also cut through time, such as cutting through the past within a timeframe of at least a dozen seconds. It allows Fukuchi to "foresee" the future, rendering surprise attacks to be anticipated and enabling him to overwrite defeat in battle.
Despite its exceptional ability, using Amenogozen has limitations, one of which is its space–time range limit. For example, if a target is too distant from its cutting limit, such as a submarine that has dived too far from a ship deck, Fukuchi is unable to cut through the space in between him and his target. Moreover, with Amenogozen's metal composition, its natural weakness is Michizō Tachihara's metal manipulation ability, which allows Tachihara to rid Fukuchi of his sword and even prevent Amenogozen from piercing through neither space nor time once controlled.