When Mistuki truly realizes her son's grown up, it doesn't have anything to do with hero work—
It instead clicks when Izuku comes over for a sleepover, and after a blood-curdling scream breaks the quiet of the night, she walks in on the boy comforting her son after a nightmare,
dynamight calling izuku “teach” via earpiece while they’re both on patrol…izuku tsking and going “kacchan, i’m not ‘teach’ right now,”…katsuki smiling, replying with “yeah? well i ain’t kacchan right now either, so what are you gonna do about that, teach?” someone interjecting