Alternate Universe Atton/Will.

Atton's possibly come straight from some sort of formal event his brother made him attend. It would explain a lot.

Firstly, why he's outside hitting a punching bag. Sitting down for a long period of time is frustrating, and difficult, and he isn't fond of it. Secondly, why he's wearing a kilt, something that is usually reserved for when he's forced to. Thirdly, why there's a very smart shirt and jacket discarded on the ground nearby.