Below is a Monster Hunter Portable 3rd Dual Blades Tree image chart.
Dual Swords (DS) are a high speed class of weapon introduced in Monster Hunter G. They possess small attack stats and are incapable of blocking; but instead possess a high attacking speed and a large variance in elemental damage and status effects (in some Monster Hunters, Dual Swords may posses 2 different elements or status effects at the same time). DSes also increase their damage output through the “Devil’s Dance” skill (akin to the Longsword’s “spirit blade”), which increases damage output and does not cancel or overlap the effects of buff items such as “Demondrug”.
Dual Swords are most notable for their “chain-attack” method of dealing large amounts of damage over time. This differs from SnS methods by creating grandiose combos or infinite strikes (as opposed to short combos which move the player dramatically).
The only Monster Hunter title to be released in the US not featuring any DS-class weapons is Monster Hunter Tri. This is thought to be due to difficulties with underwater combat or Wiimote control compatability (though some speculate that shaking the Wiimote is almost ideal given the “button mashing” required).
This image chart is specifically a Dual Blades Tree for Monster Hunter Portable 3rd.