I actually believe those guys were along Yamamoto when the Gotei 13 was called "demons" or w.e . But Yama was the strongest back then to. So I still believe hes the strongest Shinigami to live yet. (Kenpachi /Ichigo taking his place soon of course). So, I suppose the others probably left to join the Squad zero, while Yama wanted to keep the Gotei 13 strong so he stayed. ^_^ What do you people think?