You had a really bad day, you came back home to your boyfriend, who quickly understood that something was wrong as you were much less happy and active than usual.
When he asked you what he could do for you, if he could do something, you said you just wanted to be held. So that's what he did.
That's how Katsuki ended up holding you into his arms, with your legs wrapped around his waist while he walked back and forth into the living room, placing kisses on your head as you rested it on his shoulder, ending up falling asleep, wrapped up into one of his oversized hoodies, too.
One of his arms just under you to hold you up against his body, while the other hand was holding your thigh, stroking it gently and carefully. The murmurs saying 'Everything is gonna be fine' and 'I love you so much' dying right after you fell asleep, to not disturb you.