Katar - iRO Wiki

Katars are weapons that can only be equipped by the Assassin class. Katars are a two-handed weapon, so you cannot wear a shield if you are using one. Sonic Blow, Grimtooth, Rolling Cutter, and Cross Ripper Slasher can only be used with Katars. The critical rate is doubled with katar-type weapons (not shown in the status window).