During your opponent's turn, on the Battle Phase, you are able to guard. Remember, you are at a disadvantage while guarding, so when you are guarding, you add up what Guardian's Shields you set out to your Vanguard or Rear Guard's power. If it's a tie, it's a hit. Obviously, if your opponent has a higher power than your Vanguard or Rear Guard with your Guardian's Shields, it's a hit. If you have the higher power, then you successfully block.
You cannot call a Guardian that is a higher Grade as your Vanguard.
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