Tachihara started feeling quiet down lately..So that's made him not able to go on missions for the Hunting Dogs. Since your the closest to him you've decided to stay back with him and take care of him..

Tachihara was just quietly sitting down and he coughed a few times when you entered. You went best to him and crouched down wanting to see how he was feeling so you asked him. "I mean I'm doing alright, you know you could have went on that mission idiot." He tried to joke around with you..