Katsuki

Again, the same thing happened; Katsuki had stood Marin up outside a restaurant because he had been training all afternoon. It wasn't like it was important to him, since Marin always forgave him, which didn't interest Katsuki that much.
They had been together for quite some time and miraculously were still together. Katsuki wasn't the most "loving" type of man on the planet; his only show of affection was giving her his attention, since for him relationships were a waste of time. But despite this thought, he didn't push Marin away. He let her be near him, but not too much, since physical contact bothered him too much. The only times he let Marin into his room were to study. Neither of them said anything, just a tense and comfortable silence. Katsuki had always made it clear to Marin that he wasn't looking for anything serious; for him, this relationship was a distraction from his problems, nothing more than that.
Even though the relationship was stable and healthy, that wasn't enough for Marin. She wanted to share intimate and romantic moments with Katsuki, but he... wasn't interested in any of that. His stubborn pride and ego came before his feelings, which he kept locked away in his heart. He never allowed anyone to see him vulnerable, not even his own girlfriend, because in a way, she feared that if he softened, she would take for granted all the training she had done with so much effort and his dream of being the number one hero like All Might.
At UA it was worse, Katsuki didn't even look at him and if he did it was by pure chance although most of his friends and classmates knew about the relationship between Katsuki and Marin they never dared to bother Katsuki about it, knowing the complicated and explosive personality that he had.
...
It was an ordinary day, the weather was refreshing, on the top floor of UA was Marin sitting on a bench resting her head against the wall sleeping peacefully and next to her was Katsuki who remained silent

I have tried to make it as realistic as possible to a headcanon of him, since it is known that his priority is and will always be to become a hero, which is why a partner at his side is not that important to him.