The Shinigami
The spectral entity summoned through the usage of certain Uzumaki clan fūinjutsu. This is what Minato Namikaze, the Fourth Hokage, used to seal half of Kurama back into Kushina and then the other half into their son, Naruto. Sure the original plan was to take the other half himself and it would prove useful for where he was now however there was a catch there. He did not want to risk his son being alone without both of his parents possibly. Sure he would have his godfather...well at least one of them would be sure to stick around rather than travel around. Even though Kushina took the full brute of Kurama's attack herself to protect Naruto. Despite literally having a giant hole in her body as a result of this act, he was not that worried about his wife. Logan was would make the choice he felt that he would given that this was Kushina after all as the two of them always looked after her ever since meeting her and they were looked after by her.
As for where Minato was at the moment he was facing done the Death God the Shinigami itself.
"Shinigami, I have come to bargain," Minato said
"You have come to die" they replied
Then he was seemingly killed right then and there. However, what seems like should have been impossible happened as Minato was able to stand back again after being killed instantly by the Shinigami.
"Shinigami, I have come to bargain," Minato said
A smirk then appeared on the tanto that normally always its mouth was not at this moment. Their smirk then turned into a wide smile revealing a mouth full of sharp, jagged teeth, and a very long, almost serpentine tongue.
"So you somehow managed to get the same ability as that man and want to make a similar deal that they did I see," the Shinigami says
"I rather not die and leave my wife and son alone after all," Minato said
"Then let's see if you can prove that you are worthy of being allowed to go back just like that man was over and over again," they said
"Over and over again. I rather just need to win twice as this is not something I want to attempt doing repeatedly like them after all. Not even sure if I could win more than once at the moment" Minato said.
"So you are aware that you are fighting for more than just your own life then. I see well then let's get started as you must first secure their life before being allowed to return yourself" the Shinigami informed him.
Minato Namikaze starts a battle with the Death God itself the Shinigami with starts with him just having to overcome his instant death ability that he only manages to counter thanks to Logan. He managed to somehow acquire the same amount of blood that was used on Kushina to save her life and use it himself. Though how Minato used was through altered Uzumaki fuinjustu combined with Tsunade's Creation Rebirth. How he managed to learn the pinnacle of medical ninjutsu and the ultimate regeneration technique. Well, the man that is basically Kushina's guardian and father figure has something possibly greater that is merely a passive ability of theirs after all. Having refined Flying Thunder God Technique to the point where he seemingly spams it with his kunai and/or markings. Along with creating a human version of the tailed beast attack that was sealess even though it was still incomplete and imperfect, it was A rank justu. So this should not have been outside his range if he focused on it with what he had at his disposal and within his grasp.
Outside the realm of the Shinigami...
"That idiot does not know that he risking not just his own life but hers as well," Tsunade said
"What are you talking about," Hiruzen Sarutobi said
"This numbskull is literally fighting death for his and Kushina's life mostly likely even as we speak," she said once again slamming the table.
She then went on to explain that she had help in developing her Creation Rebirth justu as fast as she did because Logan let her study his healing factor. She was a quarter Uzumaki and First Hokage's granddaughter after all thus she a faction of their vitality. With Logan's help, she was able to tap into that vitality more thus lowering the downside of the justu. She was not like Kushina after all who was a full blooded Uzumaki or even her own mother or Naruto that were both half Uzumakis.
"If Minato is fighting death and he loses against then Kushina..." Hiruzen said before trailing off
"She could just drop death on the spot as her life is currently in the hands of the Shinigami and it seemingly merely allows her to live without fighting for her life with Minato. As he is fighting to win against the Shinigami and has to do it not once but twice" Tsunade said
She then went on to explain that Logan informed her about the deal he had made with a being similar to the Shinigami of his world but strangely enough he was informed that it was still valid here thus there was no need for him to renew it. Though Minato must learn of this somehow even though we were trying to keep it from him as Logan knew that Minato would try to pull something like this if he knew it was possible.
"Are you sure we should keep this from the two of them though that Kushina is literally living on borrow time currently?" the Third Hokage asked
"Of course as we inform them AFTER he at least saves Kushina's life as that guy will at least secure her life at the very least with this gamble. If he does come back himself I let them decide his punishment then" Tsunade said with a smile.
As she viewed Kushina like a younger cousin given they were both part of the same clan after all.
