"Explaining a joke is like dissecting a frog. You understand it better but the frog dies in the process." — E. B. White
That said, read the following only if you wish the joke to die, because I am about to dissect it.
There is a famous quote--nay, exchange--on the Internet from Princess Bride, in which Inigo Montoya is fighting the Man in Black, and after a spell, admits his opponent is better than himself. However, he subsequently informs said opponent that he is "not left-handed", whilst swapping his blade to his right-hand. Now, as he had been fighting off-handed up to this point, his sudden, remarkable increase in skill single handedly turns the tide of the battle.
Montoya's opponent also does this, in the same battle, with near identical results. It is from those two instances of the trope I appropriated the lines given to Nanoha.
Now, Nanoha is left-handed. I know this, you know this. This is, to MGLN fans, well established fact, and she fights all her battles using her left hand. The artist of the image we are discussing, however, is either not aware of Nanoha's handedness, or forgot.
Because in this image, Nanoha is wielding Raising Heart in her right hand.
