As far as i know it is to denote big brother or a superior man much like prolly Senpai but less formal.... Hence the term is used to call the wrestler (also a pornstar) Billy Herrington in Japan. Prolly because of his excellent physique and wrestling prowess (? - open to debate) and not for being a pornstar hehehe. As for the Yakuza aspect... well I have no idea one must prolly be well immersed in the culture/life in Japan to fully grasp why.