The first host of Shukaku was a man who's name was lost to time, and his identity swallowed by his companion. But those who witnessed his birth knew him as "Bunpuku". He started life as the youngest son of the youngest son. Without any chance of inheritance amongst his clan, he sought a life with the priests of the Wind Temples. Suna was young then, a fledgling bird yearning for the vast resources it saw as its own.
Konoha had staked its claim as a conglomerate of powerful clans, and the desert-dwellers were unnerved by the shift in balance between them. The fabled Beast of Shukaku lurked in the northern wastelands, and whispers carried forth of a ritual that could bind the power to a human host. Bunpuku was selected from many, for his talents in chakra manipulation. Many believed it would be an honor, and they would quickly change their minds.
A seal was created, and the boy was drugged. A small army went to face Shukaku, although they knew they could not kill the beast, merely seal it away. Even that process claimed a share of lives, and by the time the winds stilled, there was more blood than sand to the naked eye. Bunpuku sought inner peace, as he always had. But the first night he tried to sleep, half of the largest Wind Temple was destroyed.
He was immediately an outcast, and reviled in normal society. So he roamed the deserts, with only incoherent mumbling in his mind. When Suna requested him, he answered. They recovered swathes of territory stolen from Iwa, but their weapon was a double-edged sword. Shukaku took lives indiscriminately, and in fear and helplessness the desert people stayed away, and the first Kazekage began to mimic the One-Tail's abilities. When the time came to capture the Jinchuuriki, he would be ready.
The Priest came to view the One-Tail with some kind of fondness. Ah, he was a demon, yes he was monstrous. But Shukaku shared his body, and in their lonely wanderings, the bijuu became his only friend. As seasons past, and Suna began to expand its dominion, their endless nomadic life had to end.
Bunpuku willingly handed himself over when the Kazekage requested it, and saw his new cage as the perfect place to meditate in peace. Shukaku taunted the old man for his weakness and compassion, even for the Bijuu who ruined his life. Bunpuku always smiled, as if they were having a friendly chat. He kept smiling even when the guards forgot his real name.
"You're exceedingly nauseating."
"Thank you, Shukaku."
"It doesn't bother you? To have them forget you? Cage you up like me? Spit on your grave when you finally kick the bucket?"
"No."
"…Why?"
"Because you'll remember me. That will have to be enough, and I don't regret my life."
"…You remind me of someone… The Sage, I guess."
"…"
"You better not be about to cry on me, old man."
"No… Thank you, Shukaku. I think those are the kindest words you've ever given me."
"Pfeh, don't expect it again."
"I don't need to hear it again," Bunpuku smiled. "I never forget."
"…Niether do I."
"Glad to hear it, my friend."