Hasso is a Samurai job ability gained at level 25 in Final Fantasy XI. It may be used once per minute and will remain in effect for 5 minutes. It cannot be active at the same time as Seigan, another Samurai ability. If Seigan is used while Hasso is active, Seigan will overwrite Hasso, and vice-versa. It improves Strength, Accuracy, and grants a small Haste effect while using two-handed weapons. It will also impose a penalty on casting time for magic, singing, and Ninjutsu if those are available via Job or Support Job.
At level 25, this will add +3 Strength, +10 Accuracy, and +10% Haste. This will improve up to level 75 where it will add +10 Strength, +10 Accuracy, and +10% Haste. The bonuses offered to another job with Samurai as a support job for using Hasso are equal the level of the active subjob. IE: A DRG50/SAM25, would gain +3 to STR, a DRG75/SAM37 would gain +5 to STR, but a DRG75/SAM25 would gain only +3 still to STR. In all cases, the full +10% Haste and +10 Accuracy are given.
Hasso (八双) is a stance where the sword is held perpendicular to the ground and is used for various diagonal cuts such as Hasso Kesa Giri (八双袈裟斬り), which is a diagonal cut starting from one's shoulder. Tenzen is standing in Hasso when engaged.