well... there is another point of view... when kenpachi killed yachiru's parents, and when he fought with ikaku... he didnt have shinigamis cloth... either of the three... not yachiru, ikaku and kenpachi... so i though that at that time there were not shinigamis at all... only spirits with high reiatsu in SS... and then kenpachi have already that katana... so i dont think that it is a shinigami sword... just a sword he used to pick fights....this is only based on the anime... so im not sure if those flashbacks were in the manga