[Katsuki falls silent, not from shock or sadness, but in respect and admiration for the man's last words to Yuji. They resonate with him. It's almost the same as All Might's final words before his retirement: "You're next." People thought he meant a promise/threat to villains, but only a few knew he meant Midoriya Izuku. Of course they were heavy words, and "fair" is disputable. But... both Nanami and All Might's last showed their utmost faith in their proteges to become the great sorcerer and hero they believed them to be.

It's mind-boggling to Katsuki that Yuji couldn't understand what his beloved mentor meant. To think those words were a curse or a shame on him. Yes, they were weighty for a successor to bear the mantel of someone they saw as so great and looked up to so much. At least Yuji's starting to get it, how much his teacher cared for him and believed in him.]

You don't have to say it. It comes through in your eyes and smile when you remember him.

[Whether it's the sadness glistening in them or the sparkle shining inside, the little soft smile on Yuji's lips that's tremulous in its gentle sorrow, or a brilliant grin conveying his admiring pride, it's obvious Nanami meant far more than words can convey to Yuji.]

He's an amazing mentor, and he knew he had an amazing student.

[Maybe someday, Yuji will believe in himself as much as Nanami believed in Yuji.]