According to popular legend,
Besides being a Tailed Beast, Matatabi was also the Death God's pet, tasked with squatting outside the gates of the Pure Land and guiding the souls of the dead.
Though the truth was not quite as fantastical as the legends claimed, when Two-Tails was young, she had indeed briefly served as a cat-cart driver in the Pure Land, pulling a little cart to ferry departed souls across the river.
Unfortunately, after only a few years, Old Man sent her away. However, the Sage of Six Paths had not revoked her authority to enter and leave the Pure Land.
And this special ability to travel freely between the worlds of the living and the dead
was called the Sanzu River.
At that time, Indra had just been defeated by his younger brother. Proud all his life, he naturally would not admit defeat so easily. His ideals could lose, but when it came to strength, he had to keep Ashura in check.
Thus, after years of training, he felt that his strength had reached a bottleneck. There was no one left in the world who could help him improve.
But he knew full well that he still lacked the power to utterly crush Ashura, so he turned his attention to his biased father.
Since Father could give Ashura such outrageous boosts, creating giant Wood Men and giant golden men, even teaching him how to form balls in his hands, then he could certainly help Indra take another step forward.
Holding to the belief that if Father was still biased, he would tell Mom, Indra went to the place where his father had secluded himself, only to learn that Father had long since passed away. All that remained were the descendants of his younger wife, guarding Father's relics.
Naturally,