波風ミナト
When he first saw the Fox and felt its potent Chakra, he'd known immediately that the seal would not work. Still, he'd hoped against hope. There was only one other alternative and he was afraid to take it, didn't want to take it. He hadn't expected to die so soon. He needed to live, if only just a little longer, long enough to help the village recover from the night's disaster, long enough to make sure that Naruto would be in good hands
But when he'd tried to apply the seal, it hadn't worked. He'd known but he'd still tried. His hopes had been failed. There was no other way. He had to do it. Kushina would understand. He couldn't let her perform the ritual, couldn't let her spend the rest of eternity with her soul trapped inside the Dead Demon's belly. That would be too cruel.
For the first time that night, the Nine-tails' overwhelming strength came as a blessing. The toads were being overpowered. It was perfect. Kushina would have to intervene. She would not be able to perform the Dead Demon ritual while she held down the Nine-tails with her Chakra chains, and she would have no choice but to let him do it, to let him engage in the epitome of self-sacrifice. He knew Naruto would be given what he needed, that his only son would be raised well with the help of those he trusted.
Sealing the Fox would be easy. In hindsight, he should've brought the Third with him. The old man and Jiraiya were the only others who knew how to invoke the Dead Demon. The soul to be offered didn't have to be his own.
The very thought made him feel ashamed, and he crushed that little selfish voice of hindsight ruthlessly. The options were either him or Kushina, and it wasn't going to be Kushina.
"It's too strong." He explained to her. "I'll have to split its Chakra in two. There's only one way I know how."
Kushina stared at him blankly for a moment. And then, as she finally began to understand the full import of his words, she laughed. It was a helpless, miserable laughter. "The Dead Demon Consuming Seal." She said. Her voice was resigned. She knew that he knew that she could not invoke the Dead Demon in her current state, and he knew that she wanted to refuse. But there was no time for them to argue, no time to discuss or bargain for a better solution.
He would do it because he loved her. It was something he could imagine Jiraiya writing into one of his romance novels, this sacrifice for love. The only difference was that in a Jiraiya novel, the hero always survived, and his supposed sacrifice would serve as the catalyst for earning the love interest of his intended partner. The story would then be followed by smutty shenanigans as was typical of a Jiraiya novel. But he was not a hero in one of Jiraiya's novels. He would not survive, and neither would his own love interest.
Kushina would die regardless of what he did this night, and he would die with her. He was doing it for her, he told himself. She was the reason he was leaving his son an orphan. At least this way, her soul would be able to rest in peace. At least this way, she would be able to watch her son grow like he knew she wanted.
But there was something more. As his soul was being torn from his body, he found that he wasn't being honest to himself. No. He wasn't being honest at all. He had refused to acknowledge the truth, had tried to convince himself that his sacrifice was selflessly motivated and nothing more. He hadn't wanted it to be this way, hadn't wanted his reasoning to be so petty and selfish, but that was what it was. No matter what he'd wanted to believe, the fact remained that he was ultimately driven by a petty human selfishness.
He'd chosen death because life without her would have been meaningless anyway.