Really bad

Seadrei squinted his eyes when he realized that Rain wanted to overpower him like that… he knew that Rain was impertinent, but he was supposed to be smarter than that…

In the end, Seadrei used five of the water arms to slap Rain at the same time, but a powerful blast happened before they could reach him.

The entire space quivered violently, causing the underwater city to tremble and sway. The movements of the water sent ripples coursing through the surroundings, agitating the very foundations of the city. Amidst this chaotic upheaval, Seadrei strained to perceive the events unfolding before him. In a moment of keen observation, he discerned Rain's seemingly imperceptible arm motions—so rapid that they appeared almost motionless to the naked eye, defying conventional understanding of movement.

Rain didn't expect that he would have the chance to use Perfect Block like that, but it was certainly useful with the giant ice fists.