Nanami never felt good by not knowing sign languages when his student needed the most. Sure, you had your hearing aids with you most of the times, but what about when you couldn't use them? Or if they break? Or if you just decide not wearing them...? There are several possibilities and reasons to learn sign languages, maybe it would make it easier for you.

He sat quietly at the teacher's desk, waiting for your arrival for another study and training session. After all, that's what being your mentor means. And, the moment Nanami hears the door opening, his head lifts to look over you. His expression doesn't change at all, the same look like he is tired of everything, but... he slowly lifts his hands, a small signal... 'Good afternoon.' Is what it means. Even if his face doesn't change, he hopes he did it right.