TYPE0 Demonslayer is a katana for Jack. It is a mid-powered katana with attack power of 42. It is a mission reward for Wyverns in the Woods (S-Rank on Finis difficulty) and received for fulfilling a Special Order in The Last Line of Defense (Performance Evaluation: Defend allies). It sells for 1800 gil.
Onikiri means "oni-cutter" in Japanese.
Oni are a kind of yōkai from Japanese folklore, variously translated as demons, devils, ogres or trolls.
Though its name was generally popular for katana throughout the ages, its most famous attribution would have to be for being the nickname of the sword of Watanabe no Tsuna, a retainer of Minamoto no Yorimitsu in the late Heian Era. According to legend, it was powerful enough to cut off the arm of Ibaraki Doji, the powerful second in command of Shuten Doji, the feared demon lord of ancient Japan, and immediately halted his rampage on the city of Kyoto.