Long Sword Overview

The Long Sword (太刀 Tachi) is a relatively fresh addition to the roster of weapons available in the Monster Hunter series of games. Originally, Long Swords (Also called tachi blades) were Great Swords that resembled katanas. They became an independent weapon class in Monster Hunter Freedom 2. Since then, they have become a very popular choice amongst the player base, having comparatively swift attacks, fluid controls, and relatively high damage potential with the addition of the Spirit combo.

Having moderately high attack power combined with mobility means having some drawbacks, however. Since its departure from the Great Sword family, the Long Sword has no ability to guard against attacks by any means, aside from the standard dodge rolls. Thus, the hunter must be aggressive enough to know when and where to attack, while being cautious enough to know when to cease attacks and dodge. The Long Sword has a short delay after most attacks, but balances this with a back-hop/wide swing attack (known officially as the "Fade Slash") which can be performed after any attack, allowing fluidity. The hunter must take some risks, in order to fill up his Spirit Gauge, which, once full, increases damage dealt and enables the sword to unleash a powerful Spirit Combo: a fast combo with 5 attacks that can be extended for up to 7 hits, and can be canceled out or finished at any time with a Fade Slash. 

- Weapon Traits :

Long Swords are very versatile weapons. Their handling is quite different from the Great Sword's, even though they come from the same branch. Hunters will find that one can often upgrade a Great Sword into a Longsword, but almost never vice-versa.

• Long Swords are very fast compared to Great Swords and can land hits much faster.
• Attacks can be chained together very easily. For example, triangle, triangle, circle, triangle is loop-able and helps fill the spirit bar very quickly.
• Long Swords have 2 main branches, Bone and Iron Katana. As per usual, the bone path favors elements and status effects while the Iron path favors raw damage and sharpness, though both have multiple branches.
• Long Swords have the "Spirit Blade" ability, represented as a Spirit Gauge below the Stamina bar. Every time a hit is landed, the Spirit bar fills. The amount filled is based on the power of the attack. Perform a "Spirit Blade Attack" with the R button. Performing a Spirit Attack drains some Spirit from the gauge. The first part of the Spirit Combo can be performed without Spirit, while the 2nd and 3rd swings can only be performed with sufficient Spirit. A full Spirit Combo consumes about half the Spirit Gauge.
• Spirit Attacks can be extended for no additional Spirit cost by pressing triangle after performing a Spirit Attack. This will also help refill the gauge mid-combo to earn back some of the expended Spirit Gauge.
• Spirit Attacks have ESP and do not bounce, regardless of weapon sharpness and monster armor, however, the added attacks in between will bounce normally. The extra reduction to sharpness from bouncing will still apply. 

- Spirit Blades

The Long Swords most defining trait is the Spirit Gauge. Using it correctly is vital to mastering the weapon. To perform a Spirit Attack, press the R button.

• When the Spirit Gauge is full, the hunter receives a 12% increase to attack power.
• Once the Spirit Gauge is full, it will last 30 seconds while flashing and giving the increased attack effect.
• After 30 seconds without hitting an enemy, the Spirit Gauge will stop flashing and begin to fall, removing the 12% attack increase
• Once the Spirit Gauge starts decreasing, it will take approximately 35 seconds before completely emptying itself.
• Each Spirit attack will slightly deplete the Spirit Gauge but deal extra damage. In addition, Spirit Attacks have auto-ESP and do not bounce, regardless of weapon sharpness and hit location. Please note that ONLY Spirit Attacks gain ESP.
• Pressing triangle or circle after the first and second attacks of Spirit Combo will perform an additional, unboosted attack without interrupting the Spirit Combo.

• The final attack of the Spirit attack combo unleashes 3 consecutive slashes. These 3 hits are all part of a single attack and cannot be interrupted. The only possible follow-up actions after the 3rd attack of a Spirit Combo are the Fade Slash or a dodge roll.
• It is possible to unsheathe directly into a Spirit Combo by pressing triangle and circle simultaneously while sprinting.

• From generation 3 onwards after finishing full spirit combo, you will unleash final wide slash that make your blade glows after that. The blade glows from white > yellow > red with additional damage each glow levels. The blade's glow will revert to none after red portion in spirit bar is empty

- Pros and Cons :

Advantages

• Good power
• Good speed
• Perfect for breaking monster parts and severing tails
• Spirit gauge leads to powerful and sharp attacks
• Good agility while unsheathed
• Long range
• Most times has the greatest elemental attack from other weapon types

Disadvantages

• Cannot block
• Running Speed is not as good as Sword and Shields or Dual Swords
• Cannot cancel and roll quickly during a combo
• Weaker than the heavier Great Swords (In terms of the damage done in a single hit)
• Loses sharpness faster than most other weapons 

- Generation Changes :

   

Additions in MH3

• Spirit Blade attacks consume Spirit if the bar isn't full. If it is full, however, the bar will not decrease.
• The Spirit Combo has an additional attack after performing the usual three attacks, called the Spirit Roundslash. The Spirit Roundslash is a lunging sweep attack with a wide area of effect. The hunter automatically sheathes the weapon after performing a Spirit Roundslash and gains a minor damage boost if the attack connected.
• The Spirit Meter also has different levels of power, starting with the regular level. Each time a Spirit Roundslash hits, the meter is charged up another level. There are three different levels: white (which decreases slowly), yellow (which decreases faster), and red (which decreases most quickly). Each level gives a more powerful attack buff, with red giving the most benefit. When a charge runs out, it will revert to the regular level, and the damage boost with be lost. Landing more Roundslashes with a certain charge will increase it to the next level, and landing one with a red meter will simply refresh the charge.
• The Fade Slash is able to hop to either side, not just backwards. Holding the control stick to the left or the right (with the Classic Controller) or tilting the remote on its side (Wiimote and Nunchuck) when performing a Fade Slash will move the hunter in that direction. The fade slash can only jump left or right if performed as part of a combo.

Changes in MH3Prd

• It should be first noted that the changes to the Long Sword do carry over to Monster Hunter Tri-Ultimate, and also carries over to Monster Hunter 4.
• Spirit Blade attacks now consume spirit regardless of whether or not the bar was full or not, requiring that a hunter will have to refill it or use normal attacks between some Spirit Blade attacks to sustain a high enough Spirit Gauge to complete another Spirit Combo.
• Performing the "Roundslash" at the end of the Spirit Combo will increase the charge level of the Long Sword, from white to yellow to red, no differently than before. However, in Monster Hunter Tri, if a Roundslash wasn't performed quickly enough, time and time again, the Long Sword charge would drop to none, leaving the hunter with no choice but to start all over again. In Portable 3rd and Tri-Ultimate, the Spirit Gauge has been reworked to show more information. Not only is the level of charge clearly displayed around the Spirit Gauge, but also how much time until that charge is lost. Secondly, and more favorably for hunters, when a charge is lost, instead of having to start from scratch, the charge reverts to the previous level (red to yellow and yellow to white before disappearing).
• Due to the changes made, the Long Sword has a more consistent damage than it did in Tri. Not only is it more consistent, but for skilled players, it's relatively easy to stay at a yellow or red charge for an entire hunt, after achieving it of course.
• In MH4U it's possible to do a spirit attack when fade slashing, so fade slash then spirit attack.

- Tutorial for Beginner Hunter (by GaijinHunter / @aevanko)

https://www.youtube.com/watch?v=eBUkSSbcuTk