Disclaimer: I do not own Avatar: The Last Airbender, nor do I receive any money from this work of fiction.
This is probably my favorite moment in the series, and I'm surprised everyone doesn't jump up to write their version of it.
Toph was enraged at the forced trip home and felt the walls around her helplessly. She was truly blind now. It wasn't like she could break the cage from the outside; it was too thick a barrier between her and the earth. Still, she couldn't just go back home for her parents to try to tame her back into a quiet, obedient pet. She still had a job to do.
"Not even you can bend metal."
Why not? Metal came from earth, didn't it? But they were so different. Earth could be solid rock or dirt or sand and could have all different kinds in a handful of it, from sediment to volcanic rock. Metal was metal was metal, and it was so clean. She felt iron ore one time in the badgermole tunnels. It felt like its own kind of rock, but the finished metal seemed so distant from its origin. Someone had always purified it and filtered out the rock and dirt. Still, they couldn't get all of it out, could they?
Toph gave the cage another punch out of frustration before realizing that, for a short moment, she could see. She gasped at the realization, then proceeded to strike and stomp some more. She wasn't imagining it. Every time she hit the metal, it got the earth spread throughout it shaking so that she could feel the shape of the entire cage.
Xin Fu beat at the side of the cage to get her quiet again. She huffed, but made no comment upon noticing she could tell exactly where he hit the cage. Too stubborn to pay him any heed, she struck the cage more precisely, using earthbending stances to try to move the cage, but it still stood strong.
Maybe there actually was a different way of thinking about it. If you had to be like a rock to bend earth, maybe you had to be like metal to bend metal. But how was that? Metal was harder than earth, even more stubborn than earth. But there was more to it, not just a show of brute force. Metal was strong and enduring; it didn't shatter or crumble like earth could. And it was clean. Pure.
A smile spread across her face. She took a long, deep breath and made a heavy, cathartic exhalation. Xin Fu disappeared, Master Yu disappeared, even the metal disappeared. With her mind clear of distractions, now cleaner, she saw only a cage of dirt around her. She tried breaking through its resistance now.
"Come on, metal," she urged. "Budge."
She gave a last strike, and the wall of the cage finally yielded.
"Whoo!" She shook the hand that had just punched a giant dent into the wall. "Toph, you rule," she applauded before proceeding to tear the cage open.