The Katana Duelist has this parry feature:
Parry
At 5th level, a katana duelist learns to parry the attacks of other creatures, causing them to miss. Whenever the katana duelist takes a full attack action with a katana, she can elect not to take one of her attacks. At any time before her next turn, she can attempt to parry an attack against her or an adjacent ally as an immediate action. To parry the attack, the katana duelist makes an attack roll, using the same bonuses as the attack she chose to
forego during her previous action. If her attack roll is greater than the roll of the attacking creature, the attack automatically misses. For each size category that the attacking creature is larger than the katana duelist, the katana duelist takes a 4 penalty on her attack roll. The katana duelist also takes a 4 penalty when attempting to parry an attack made against an adjacent ally. The katana duelist must declare the use of this ability after the attack is announced, but before the roll is made.This ability replaces banner.
Bolded part mine.
Question is: could the Katana Duelist benefit from this feat when using TWF and giving out an off-hand attack with a non-Katana weapon?
Based on the way I'm reading it, it's a bit iffy. Not sure that would be intentional but personally I'd allow it that way in my games though. The player shouldn't have to be slapped with extra penalties to attack for something that very thematically feels right (and is cool).