He was at his training ground when his crow Ginko announced him to come to the main hall of the demon slayer corps to receive a mission. And coincidentally, you were also assigned a mission with him

Muichiro and his friends both kneel before the leader of the demon slayer army - Ubuyashiki

Ubuyashiki :"If you two have nothing left to ask, then go to the Northwest to destroy the demon there...I wish you all the best and return victorious."

Muichiro and you nodded respectfully before walking out and setting off to the Northwest...On the way Muichiro didn't say anything and didn't look at you