The Nikana is the first melee weapon released that is used as a component to craft its more powerful version, the Dragon Nikana.
The word "Katana (刀)" refers to both the sword and the style in which it is wielded. In comparison to the similar "Tachi (太刀)", the Katana typically has a shallower curve and is worn on the belt with cutting edge facing up whereas the former has a deeper curve and is hung from a cord on the belt with cutting edge facing down. There are, however, exceptions.
Blocking involves pulling out the weapon with the blade still sheathed (similar to the blocking stance for normal longsword weapons). The actual blocking animation involves parrying with both the blade and the sheathe separately.
The Tenno fighting style with the Tranquil Cleave stance for the Nikana is highly reminiscient of Iaido, a type of martial art in which the sword is quickly pulled from it's scabbard to cut an enemy, cleaned of blood, then sheathed again, often in two or three fluid motions. In contrast, the Decisive Judgement stance is more reminescent of the Kenjutsu fighting style, which is drawing the sword and using it with both hands.