The Heavenly Sword Technique is a special set of sword moves under the Heavenly Sword Path that were deemed "too risky to use" and were treated as Forbidden Arts.
One of Xu Mei's secret Trump Cards was a special subset under that very technique: Dual-Wielding Sword Arts!
Its attacks are said to strike true, no matter what the enemy tries or however they block it. But, of course, that's only possible after mastering the Heavenly Sword Technique. Xu Mei was still far from "mastering" even one of the sword moves under there, much less the entire technique!
The only drawback to the technique is that it's very offensive-oriented, making it have almost no dedicated defensive moves. One could use "attack" as "defense," though, so it's not completely guardless.
"Ugh...!"