Board Thread:Naruto Discussions/@comment-36512555-20191224052011/@comment-25122992-20191224124148

Well, as for the living beings, I still think that the blood contract matters, at least, for the summoner themselves. I mean, Madara was explicitly stated to use his blood for the Kurama summoning, and even Second Mizukage needed the blood for clam summoning, although Edo Tensei body doesn't tend to actually bleed. Regarding Fukasaku summoning Naruto, the actual technique is called Reverse Summoning; Naruto has a blood contract with the toads of Mount Myoboku, so it's logical that Reverse Summoning would work as an opposite to usual summoning.