I’m going to guess the ability is acceleration/deceleration, judging by the bullets and the blocked attacks. In that case, considering he threw identical bullets, his weakness is controlling only one type of object at a time, and it also requires physical contact. It’s pretty similar to the Executioner from Darwin’s Game, although much more limited in application. Can he fly using that power, then? Or mess with the acceleration of gravity on himself or something?
Another possible weakness is parallel trajectories, where all the active objects have the same direction of acceleration, in which case he can’t block simultaneous attacks from differing angles. If that’s the case, he won’t have any weakness on blocking multiple types of objects, which would mean attacking with two different attacks from the same angle would be ineffective. It’s also possible he could reflect any projectiles, but on the other hand it seems his acceleration might have a fixed force strength. It can fling bullets of low mass fast, but only momentarily stop Yuuri’s kick (her leg isn’t frozen on contact with him, she can move again after blocking).
Another possibility is from Yuuri’s leg block, where she recovers. It may also indicate a cooldown time for his ability, or he would have flung Yuuri away with the ability.