斬魔刀 [zanmatou] or 'beheading magic/demon blade' in Japanese. See also the weapon of the same name.
Final Fantasy Tactics

Obtain: randomly from one of the following Errands: Gariland Magick Melee, Mount Gulg Mother Lode, Zaland Embassy Antiques, Abandoned Mine, Clockwork Faire, Salvage Expedition, Zerro's Challenge, Guard Duty, Yardrow Melee, Gleddia Isle, Lettre d'Amour, Count Minimas (1), Count Minimas (2), The Durga, Endless Caverns, The Falcon, Father's Nightmare, Himca Cliffs, More Coal Miners Wanted, Ore of the Gods, Past Glory, Rhana Strait, True Romance, Zerro's Return, Zerro Strikes, Zerro Strikes Again, Appraisal, Gysahl Greens, Historic Revolt, Lionel Emissary, Second Coal Mining Expedition
Type: Artefact
Description: The indecipherable script engraved into this enchanted blade identifies it as the weapon once used to slay a demon in a single blow. It is a talwar-type sword of immense size.
Category: Item