Warning:Article may or may not contain SPOILERS from the Naruto series. Read at your own risk!
The jinchūriki (人柱力, Literally meaning: "Power of Human Sacrifice") are humans that have tailed beasts sealed within them. They exhibit extraordinary powers due to the immense chakra reserves they possess.
According to the Naruto series, jinchūriki are typically lonely and miserable people, as they are often shunned and discriminated by their fellow villagers, who view them as the tailed beasts themselves.
Though never mentioned in the spin-off, Gaara was the jinchūriki of the One-Tail in the Naruto series. However, due to certain events in the series, Gaara lost his jinchūriki status. It is unconfirmed if these events happened in the spin-off and if Gaara may or may not still be a jinchūriki.