Their relationship is initially offsetting. It niggles at the back of his mind, the way Mustang treats him.
Like that one time he'd been stranded alone in the rain on a street corner. He hadn't expected the colonel to answer the phone, let alone drive out to pick him up.
Or those times the man covered for him or took responsibility for Ed's screw-ups.
The day Ed woke up in Mustang's car after exhaustion had put him to sleep in the man's office.
How the colonel had handed over part of his lunch to appease the blond's growling stomach. It reminds Edward of something from long ago.
The time Roy hadn't commented on the tardiness of his report when Ed was having a crummy day.
The way Mustang always seems to keep an eye on him, like Hughes does to Elicia, subtly looking out for the younger.
It's not always obvious. But the stern reprimands, wry smiles, familiar teasing… It makes him uncomfortable, but also fills a hole he hadn't known existed. When comprehension hits him, he stops talking and Roy stares at him.
"Something wrong, Fullmetal?"
Edward hesitates, then, "No." And, belatedly, he realizes how much he means it.