Masaru catches young Katsuki being mean to Izuku and yells at him, but Izuku is so used to Katsuki screaming back at Mitsuki that when Katsuki starts bawling and apologizing to Masaru he's shocked into silence.
Izuku who shuts katsuki up whenever they’re arguing through the innocent act of enclosing his big hands around katsuki‘s small waist. He‘s not even trying to get katsuki to back down because he would NEVER do that to kacchan, it‘s just that…his waist can be so distracting.+