Nitōryū

The Nitōryū (二刀流, Style of Two Swords) is a form of combat designed by Arien as the unity between and  Kenjutsu. It is also famously known a the due to uniting two remarkably different forms of combat into a single, perfected form.

Description
The Nitōryū is a form of swordsmanship that, as its name suggests, makes use of two swords. Specifically, the user wields a consisting of a  and  in order to balance out the weight between both hands. Ambidexterity is considered the key to mastering this fighting style, given the difficulty in wielding one sword with both hands. Both excellent physical fitness and coordination are absolute necessities for the competent use of this style, making most candidates who aren't devoted to its mastery unsuitable for its use.

Being a combination of Samurai and Shinobi Kenjutsu styles, it is evident that the Nitōryū's very existence is almost paradoxical. This is expressed by the different methods in which Arien makes use of both swords. The wakizashi, a blade commonly employed by Shinobi, is made use of as a surprisingly heavy weapon — specifically exclusive to Arien's blades — therefore being used primarily as a means to disorient an enemy's stance with swift, strong strikes in tandem with one's chakra control. On the other hand, the user wields a katana, a weapon commonly employed by Samurai. However, Arien's use of it is for slashes that are blindingly swift due to the lightness of the katana. The duality that exists within both swords is adopted by the movements Arien takes within this style. A mixture of stability and uncertainty, a change in Arien's rhythm is extremely common while making use of this style, causing most conventional tactics of any combatant to prove simply ineffective in face of his superior skill.

Trivia

 * The name, Nitōryū and its nickname, Nisei Ichi-ryū were both inspired by, but fitted for Arien.