Rinne Tensei Questions
I have some honest questions about the Rinne Tensei technique, because I think this technique raises some problems in the manga where people could have resurrected the ones they cared about, but didn't do it. Here are a few questions that come to mind with this technique?
Does it have a time limit? In the invasion of Pain arc, we see that Rinne Tensei returns souls to the recently-deceased bodies. Kabuto mentions that some of the remains he's found were pretty badly decayed over time (so we know bodies DO decay in this universe like normal). However, Madara died about 20 years ago. When Orochimaru resurrected Hashirama and Tobirama, they had been dead for much longer. So, is there a time limit? If Madara intended to be revived with Rinne Tensei, it has to be available AT LEAST 20 years after the person died, and must allow for the body to have been decayed by that point.
Does it require the body to be available? If so, does the body still have to be in good condition? How would Obito have stopped Madara's body from decaying? Why wouldn't Obito try and retrieve Rin's body and preserve her too, just in case? Nagato was able to revive people in konoha who had been stabbed, ripped apart, trampled by gigantic monsters, burned in fires, and killed in other horrible ways. How was he able to resurrect these people, if the body needs to be in good condition?
Why didn't Nagato use Rinne Tensei to revive Yahiko? He's had the rinnengan almost for his entire life, he clearly has the ability to use the technique, and Yahiko died AFTER Madara. Even if there is a time limit, Yahiko's death must be under that limit (or it would be impossible to resurrect Madara too). PLUS, Yahiko's body was obviously kept in pretty good condition as one of the paths of pain. Why didn't Nagato bring Yahiko back to life with Rinne Tensei?
Why didn't Nagato revive his parents? Same question as above: Nagato had the means and the motive to revive the people he's lost, and he has plenty of opportunity. We have a contradiction: Nagato is the master of life and death, and can apparently revive people at will (and in large numbers), but he's let his life be defined by the deaths of a small number of people around him. Nagato's parents were dead longer than Madara was, but only by about a decade.
Why didn't Obito revive Rin? Why didn't Obito ask Nagato to resurrect Rin, in exchange for teaching Nagato cool new techniques? Obito could have used Rin as an example to teach Nagato about Rinne Tensei. After Nagato died and Obito got the Rinnegan for himself, why didn't he try to revive Rin himself? Rin died only shortly before Madara did, so even if there's a time limit Rin's death might still be inside that window. Obito should have tried to heal her, save her, or revive her and he never did. Why?
Why didn't Madara revive himself? We saw Itachi embed an MS eye in a crow and program that crow to use Kotoamatsukami in response to certain events. Why couldn't Madara have done something similar with his eyes, put them in an animal and program that animal to revive Madara at a certain point? Can a crow use Kotoamatsukami, but not Rinne Tensei? What are the rules for which eye techniques a crow (or other animal) can and cannot use?
Maybe the answers to these questions are "Whatever, plot no jutsu. STFU", but I really think this is a pretty big hole in the story that really needs an explanation.