Shin waited in the duelling ground—the sword he got from Elior last night in his arms—not that he hoped to use it in this match. He had duelled with Elior on many occasions, and although, in most of them, Elior used an easy hand, it did not limit him to feel the strength and control Elior had over his ability.
Shin had seen him burst one's arm into nothingness—like popping a balloon. He himself had been through his demonic training, all the tension he put him through. However, back then Shin was not sure how difficult it was for Elior, but later when he learned to control waves a little, he could guess even a guardian might fail to such subtle control like his brother.
