Seadrei's reaction to Rain's words was one of frustration and anger. The implication that Rain wouldn't engage in a serious battle stirred a bunch of emotions within Seadrei. He found it not just annoying but deeply humiliating.
The notion that Rain might hold back or not fight with full seriousness against him was a significant blow to Seadrei's pride and honor as a warrior. It was an affront to his status and abilities, almost insulting his prowess and capability as a fighter. The idea that Rain might not consider him a worthy opponent worthy of his full effort was a considerable source of frustration and resentment for Seadrei.
"... Very well, I find your method stupid, so I shall make you understand that through brute force," Seadrei said after lowered his stance and pointed his spear toward Rain.
