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Yuki's mother Meimi, a Magical Girl who gets introduced in the act of "accidentally" stealing a set of huge kitchen knives but doesn't even need them to effortlessly defeat a ninja, definitely qualifies.
Claw-fighting Nepeta from Homestuck begins this way, in contrast to creepy hulk Equius. Perpetual Cat Smile and kittenish behavior, but like Equius has actual combat experience, from fighting the monstrous creatures of Alternia. Unfortunately she's outleagued so early in the game that she doesn't even get a Worf Effect moment.