When Minato summons the Shinigami to seal Kurama into Naruto, he summoned the Soul King from his palace.Impressed by Minatos world and the man's will to save innocent lives at the cost of his own and reluctantly his families, the Soul King gives Naruto a gift.As Naruto grows he gains a family by that gift. Not that he didn't already have someone he called as father, even if they weren't related by blood.
Or where Naruto has a summoning contract/bloodline that summons Shinigami from the Bleachverse.
I don't own Bleach or Naruto.