The strength boost is based on the level of the Samurai increasing by 1 STR every 7 levels (at level 25, the boost is +3; but at level 84, the boost is +12).
When Samurai is set as a subjob, the value is based on the sub level, i.e. a DRG85/SAM42 will have a boost of 6.
A level 84 Samurai will gain a boost of +12 STR, +10 Accuracy, and +10% Haste for melee attacks.
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.