Board Thread:Theories and Speculation/@comment-30168130-20161223235115/@comment-734582-20161230101214

BeyondRed wrote: To me, the fact that we see Obito's chakra emerge from his ashes and enter Kakashi establishes that it was something he could only do because he had just died moments ago, perhaps because his chakra hadn't yet faded from his remains. Otherwise there would be nothing stopping him (or anybody with a suitable technique) from leaving the Pure World and possessing people whenever they felt like it. Not even hagoromo could easily return to the Shinobi world. I think it's got to do with the fact that Obito was still in Limbo (IE Nagato resurrects thousands from Limbo, but beyond limbo we've only seen a single person be resurrected). He was dead, but his soul was still bound. Presumably the fact that Kakashi had his chakra in him for decades helped (IE it's probably why Obito makes the "our chakras connect worlds" comment).

Namikazenaruto9 wrote: Yet kakashi did got wornout, nor did he volunteer to take everyone back before haogormo could summon them back. Their was definitely some limit Kakashi didn't get the chance to offer a return trip. The moment they were wondering how to get back, they got summoned back.

I think the time limit is rather that if a soul possesses for someone for too long, the possessed dies. This seems to be backed up by Obito suffering no side-effects from giving Naruto three Biju, despite the fact that it's supposed to be lethal (and even though he has the Gedo still in him, it would at least create some feedback). There's no definitive proof for it. But it doesn't change anything about the fact that Obito willingly ended his possession of Kakashi and that Kakashi didn't collapse until Obito left him.