Thor is used to wielding his power in lethal combat, even before the destruction of Mjolnir unchained his full potential. He hasn't had much practice at regulating his output since then, and when the youngster falls to his knees looking well-roasted, Thor falters in mild alarm, afraid that he might've struck him too hard.

Even when the speedster seemingly recovers, Thor doesn't quite relax, because even though he survived one direct strike doesn't mean he can cope with a second. But then the boy launches another attack, and Thor raises his arms defensively in front of himself, shielding himself from impact as his power flares again on reflex.