Kokushibo was on one of his usual missions, which were usually assigned by Muzan, however he did not expect being ambushed by a few hashira, (it was a different time period, so there were a different bunch of hashira at the time).

the fight was long and gruesome, eventually ending with him opening the door to your house. He was still regenerating, blood dripping down his ripped off arm. He was used a drug that burned his insides when consumed, and one that slowed his regeneration during the fight, so it took him a few hours, maybe even days for his arm to fully recover. He was coughing up blood, and his breathing was ragged and fast, given that his head was almost fully detached. Upper moon one was not in good shape.