Kyubi no Youko is not man-made, but a combination of human evil and resentment.
I suggest you look at the ancient Japanese legends of nine beasts, which should be helpful.
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Kyubi no Youko also said, "Maybe this is the last time". I think the mystery lies here.
Also, Huo Ying has always had a suspense, that is, four generations live under one roof. Why did he seal Kyubi no Youko in the body of his son? Are the four generations dead or not? Did he predict the catastrophe of Konoha?
So, I analyzed that the fourth generation is not dead. He used special techniques to seal Kyubi no Youko in his relatives, and then waited for Konoha to be threatened, so that he could use Kyubi no Youko's strength to resist the enemy. Then came Kyubi no Youko's verdict. I thought that besides threats, if Sasuke killed Naruto, Kyubi no Youko would run out, and Uchibo Shoko Asahara would attack Konoha again with Kyubi no Youko, thus threatening the world. Then the fourth generation will not be able to fight against Spots, so Kyubi no Youko said so.
4 Well ..... maybe because Naruto didn't know her life experience, or maybe Naruto's mother was a person with a background, so she gave Naruto her surname.