Can Opener

Can Opener is a sickle and/or knife combat technique that deals relatively small damage (1d4 non-exploding) but can create a weak point in inflexible armor upon a successful hit (1d20, and that number is now weakened). During another non-Can Opener attack, the attacker can roll 1d20, and if the roll matches a Can Opener on that entity, the opponent has base AC (13+DEX mod) for that hit. Can Opener can activate multiple numbers per enemy, but cannot be stacked and has no effect besides damage when the same number is rolled. Can Opener can be learned at a dojo.