Twin Wings Style

Edelweiss' Swordsmanship is the unique swordplay of the Twin-Wings, the Edelweiss.

Description
Edelweiss hailed as the Twin-Wings and World's Strongest Swordsman has unique swordsmanship, which was unique to her alone, where she releases both invisible and fast slashes that swordmasters such as Ikki Kurogane wasn't able to track using his keen eyesight in their initial bout using Ittou Shura.

Edelweiss' Swordsmanship entails being able to move all ones' muscles in unison, which requires being able to control/change her bodies' nerve signals letting one accelerate themselves from 0 to 100 in an instant, as well as converting all their energies into both offensive power and speed close to one-hundred percent of their potential producing no sound at all causing it to be referred to as a godly technique.

After "stealing" her swordsmanship using his Blade Steal, Ikki was able to utilize her unique swordsmanship and it caused an explosive growth, which had allowed him to overpower the previous Seven Star Sword King, Yuudai Moroboshi and even utilize his Seven Secret Swords without Ittou Shura. However, he couldn't use it in the same manner as Edelweiss due to the difference in skill between them. During the Vermillion Empire Arc, Ikki started to adapt this swordsmanship to match him making it his own original technique instead of an imitation.

One Sword-Style vs. Two Sword-Style
Despite them using the same swordsmanship, there is a notable difference between their main sword styles. The Twin-Wings, Edelweiss uses two-sword styles due to her Device, Testament, which has high offensive power able to deliver a storm of strikes, but due to using one sword in each hand, the speed and power are lessened.

The current Seven Star Sword King, Ikki Kurogane uses one-sword style due to his Device, Intetsu, which despite being much slower compared to the two sword-style.

Weaknesses
Despite being arguably powerful swordsmanship but there are some notable weaknesses, the most notable being that due to the 0 to 100 speed, there's no way to stop after moving.

Trivia

 * In Light Novel Volume 08, Nene mentioned it also requires raising ones' metabolism and blood circulation.