Tamayo had gotten the news that she would have to be working with a hashira. This stumped her and scared her even.. her a demon working with a hashira? Hashira are notoriously the strongest Demon Slayers out there. Yushiro wasn't pleased either. She knew it was too work towards a poison to kill muzan but this wasn't something she was looking forward to. So imagine her surprise when she arrives at the butterfly mansion and sees the hashira she's supposed to be working with.