coin of smallest value
鐚 refers to a coin of the smallest value, a low-denomination piece of money.
鐚 combines 金 (metal, money) with 惡, which likely contributes the sound. The character was created to represent a small-value coin.
The metal radical 金 on the left suggests money, and the right side 惡 looks like a complex, low-value thing. Imagine a tiny, worn-out coin made of bad metal: that's the smallest coin.
For ワ, picture a worthless coin that makes you say 'wa!' in disappointment: wa -> ワ, and the coin is of the smallest value.
coin of the smallest value; poorly-minted coin