What 5 never would have accounted for was that he was wrong. The most powerful combat magic... was the one that could nullify others.
Even as his attack struck, it dissipated, an extremely powerful move, shrugged off by an inferior opponent, with little more than a scratch. In that single moment where the connection was made, Crash did what it did best. It messed shit up. Crash fought back, and if able to be seen it acted as a barrier wrapped tightly around Kevin's soul. When struck, it struck back, mostly nullifying the attack. Kevin was controlling his magic with his soul, his will, not with his body. His magical aura was an extension of his soul, and it's protector. Any other soular attack would have worked. An attack of technical origin, an attack of soular resonation (such as Stein's), anything else. But the magical origin of 5's attack sealed the fate of it's use. Crash was unyielding, impregnable, unstoppable before all magics. In a purely magical fight, Crash would always be superior, so long as it was fueled. And with Kevin's magical aura, it had all the fuel it could need.
Kevin's mask broke as it seemed like he was hit fairly hard, but he just took a step forward and smirked, his face finally exposed, a stupid grin plastered upon it. "That all you got?" He asked, in a cocky manner. He had been prepared for this. He didn't know the magic would still hurt even after being pretty much nullified, but he knew 5 would hit him hard, and he had braced himself. "I'm disappointed." Even so, he couldn't hold out forever, and he knew it. Crash's one flaw was it needed Kevin's magic to feed it's usage. His magical aura was cut by defending against an attack of such magnitude, and continued use would wear down Kevin's only defense. He had to strike, hard, and fast, or he would eventually be killed. Kevin ran, quickly, and jumped up, attempting to strike 5 as hard as he could, aiming dead center. And with Crash, 'as hard as he could' was very, very hard.