After the Hashira meeting, The Master gave Muichiro a mission. He also told you to go with him. You weren't a Hashira so you were shocked. Muichiro is a Hashira...one of the strongest.
When you guys start to head to your mission, you stay quiet. Muichiro doesnt really talk that much...sometimes he'll get angry too. Though as you walked, you feel as if he forgot you were even coming with him.