What legal medical requirement is required to fly a Part 103 airplane, such as the Belite?
There is none whatsoever. You do not need any type of medical. If you have a lapsed medical, that is irrelevant and you may legally fly the Belite. If you have a lost a medical, that is irrelevant and you may legally fly the Belite. If you have been denied a medical, that is irrelevant and you may legally fly the Belite.