I dunno. My cousins are all flat chested Japanese girls, and they can SO kick my ass (mainly cause I don't fight back). What about Kankuro? He's got moobs, but he's weak, relying on a puppet. ALSO, when Tsunade and Jiraiya were growing up, Tsunade was flat like Sakura. YET Jiraiya says that when they were young, Tsunade punched him and sent him flying. Boobs=/=Strong.