Sorry I'm still pretty new to bleach. The wiki says "While Shinigami can be injured and "die" like regular Humans, it takes considerably greater injuries to kill a Shinigami than it would to kill Humans. Decapitation is the only guaranteed method of killing a Shinigami." But when ichigo is training with kisuke, before he finds out that kisuke has a zanpakuto, he asks himself why he's running away if kisuke doesn't have a real zanpakuto that can cut him. And then when ichigo fights zenpachi ichigos sword at first can't cut him. Was it simply because zenpachi was that much stronger or did it have to do with ichigos sword? Can someone give me some clarity?