At the end of Full Metal Alchemist, Ed gave up his ability to use alchemy to save his brothers soul amd body. The only way to gain something is to give something equal or greater. After it is all said and done with Naruto could possibly give the Shinigami the other half of the Kyuubi's chakra to gain his dads soul and body. Which would also explain why he told the Kyuubi he's not going to treat him bad. and why Minato said jinchuurikis can't use the Dead Demon Sealing jutsu