Wind Running

When Reborn arrives at the Sawada house to place the title of a Vongola boss candidate on an unsuspecting boy, he expects a useless teen. He wasn't disappointed but why does the boy disappear to the roof of the house and stare at the roofscape around? And why was Dame-Tsuna clutching his leg like that? One that seemed to have a limp? (Parkour Tsuna)