Miles doesn't mind going without his shirt, it would seem.
Utilising his cybernetics and systems, Miles is easily able to regulate his temperature to be perfect at all times! Whether frigid tundras, or blazing deserts, this cyber-rabbit doesn't seem too phased at all. So really, who needs a shirt? Maybe just for the fashion, but one could say that going without the shirt is equally fashionable in its own right~

Miles' muscles are synthetic - much like the rest of his cybernetic frame, but by no means does that indicate he is weak. On the contrary, he may be stronger than anyone else with a similar physique, able to lift boulders with ease! He may often use this as an excuse to help anyone with work revolving around heavy-lifting, usually asking for nothing in return. With an attitude like that, who wouldn't want to take him up on his offers?

It should be of no surprise that Miles may want to show off his cybernetics more clearly for those he meets, so occasionally doing away with his shirt is a no-brainer. It is quite a conversation-starter, after all!