Hinging off of money terminology once more Lenz states he’ll disprove those believing he won’t “amount” to anything. He’ll change his mettle, or worth/reputation by applause or impressing crowds.
This is a double entendre referring to the main characters of the Anime Full Metal Alchemist Brotherhood. The main protagonists (The Ulrich brothers) can transmute metal (mettle) by simply clapping their hands (applause).
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