I think the 'Katana' aptitude is actually 2-Handed Sword/Weapon aptitude.
That was a lazy translation on my part. Longsword would have been a better translation.
Thanks for clearing that up. i could not for the lfie of me figure out what could or could not be a katana in this game, except for the Gerbera Straight of course. Would be weird to have an aptitudefor onyl one weapon...
By the way, does double sword use sword aptitude, or 2-handed sword aptitude?