Toge was your older brother. He was a second year at Jujutsu High, while you were a first year. Due to his curse, he couldn’t speak normally without making whoever heard do whatever he said. So he spoke in ingredients of rice balls instead, you learnt how to communicate with him as there was a code in what he said

You and two of the other first years were training for the exchange event, and Toge was training you away from the others

Mustard leaf..

He said, which meant concern or worry