Fugaku forgoes all decorum and poise and simply covers his face with his hand, shoulders drooping scandalously low. He doesn't want to know. He really, truly doesn't.
He swiftly rearranges his priorities when his senses sound the alarm, warning him of incoming danger. He removes his hand only to find yet another terrifying sight.
Mikoto is smiling perfectly politely and in a manner that suggests she is both proud of their smug four year old son (which he picks up on) and also planning to murder whichever one of them is fool enough to admit to going against her wishes and teaching Katsuki to access his chakra.
Itachi mirrors her terrible smile but with a subtle nuance that indicates both his own pride (which Katsuki also picks up on) and his complete and utter innocence in the matter. His tilted head implicates Shisui, whom had just dropped Katsuki off with a hasty apology and adamant denial of his involvement before using his signature speed to escape. If only Fugaku could do the same.
His lovely wife widens her smile, expressing her doubt and humor at the idea. Shisui is too scared of her to actively piss her off, given what happened last time with Itachi and the bathhouse, and shrewd enough to surmise running would only makes things worse.
Itachi inclines his head, accepting that rebuttal, and then turns his faux smile on Fugaku, the traitor. When Mikoto follows suit, Fugaku mentally curses and scrambles for a solution that doesn't end in disembowelment.
"Katsuki," he hurriedly calls, pausing only to cough into a balled fist. "Where did you learn to do…that?"
Grinning maniacally, his youngest replies, "I figured it out on my own!"
"You accessed your chakra without outside assistance?" Fugaku latches on, desperately.
Katsuki scoffs. "Of course I did! None of you wimps would teach me, but I didn't need your help in the end anyway, ha!"
"That's incredible, otouto," Itachi tells him sincerely, practically beaming- or as much as an Uchiha can be said to do so.
"My Katsuki is such a smart boy," Mikoto praises, laughing demurely when Katsuki flushes and turns away, embarrassed.
For his part, Fugaku simply breathes a sigh of relief and makes a mental note to make Shisui Katsuki's personal guard for another month as punishment for dropping this bomb in their laps and then fleeing the blast zone.