Great game! Interesting concept, I guess it's one time use because we're using old muskets, I see the attack on titan inspirations from this from giants to being surrounded and needing a timed coordinated attack when they're perfectly in range.
The others have already mentioned that it's hard to calculate the range of the giants, it's not a huge problem, but the last level, I think, or at least the third level doesn't seem possible to win, the giants are never close enough to become highlighted and even a step closer they will destroy the building they on and lose.
On another note, when the quick time event occurs, it's much quicker to just spam random keys and watch them all fall down really quickly, it's really satisfying, but it's probably not intended? Well, most people would probably carefully press the right one, but it doesn't seem like there's consequences for pressing the wrong keys.
Great job on the game! The UI, music and voice overs are good and a nice touch, though a few more voicelines wouldn't hurt to make it less repetitive.