|This article is about a/an weapon in Kamen Rider Zero-One.|
This katana has been in Horobi's possession since he was hacked by Ark and was turned into a terrorist. Being a regular katana, it is mostly used by Horobi in his Humagear form for quick combat, but is never used in his Rider form. The blade of katana is strong enough to cut off a bullet, and leave a wound on Geiz Myokoin's body, who was a skilled fighter.
The katana was used by Horobi to initiate his first transformation into Ark-Scorpion, and was still not used in actual combat.
The katana was later used by Kamen Rider MetsubouJinrai along with the weapons of MetsubouJinrai.net's Riders. It was also used by MetsubouJinrai to end the Riders' physical forms.
During his first transformation into Ark-Scorpion, after inserting his Progrisekey into the Zetsumetsu Driver, Horobi stabbed the ground with his katana, which initiated the transformation as a puddle of material representing Ark's malice which started erupting from that spot. The katana was absorbed into the puddle, and the Ark-Scorpion Rider Model was formed, which continued the sequence.