Probably a stupid question but...

[The Walrus]

What exactly does the Double Saber's action do normally?

I know with the gear it does a tornado thing but I have yet to find anything out about what it does without the gear.

[Narugami]

Make you look pretty :D

[IndigoNovember]

Pretty sure it only does something when you have a gear. That being said, it looks like Double Saber Gear is a must get if you intend to use Double Sabers, similar to how you have to get Sword Gear to make the most out of Swords.

[Geistritter]

I hope you have better reasoning for that than "the gear exists", because Partisan's is far from a must-get even if you like to use Partisans, and it works similarly to Double Saber's.

[IzzyData]

It seems to be like block reversal. You do it right before being attacked and you will avoid damage and attack back.

Unless that was a weird fluke I've been doing.. I've only tried on twin daggers so far.

edIt: upon further testing I have found this skill to be incredibly dynamic and can be used for many purposes.

It can reset your attack chain so that you can use your first PA at any time. It also shoots you into the air a little bit which can be used for either combing in the air and staying in the air or getting you higher into the air for attacking flying units.

Loving it so far.