Becoming a Jinchuriki

The Four Symbol Seal

The Four Symbol Seal is an Uzumaki hiden technique, in the Uzumaki tree under Hiden: Sealing Release (awakened by Sealing Release DNA from a Ninja Scientist), then Adamantine Chains (level 35, 5 points, Ninjutsu 15), then Four Symbol Seal (level 60, 6 points, Ninjutsu 20).
Rank: S. Cost: 3,000 chakra. Hand signs: 12.
It must be charged all the way; otherwise it fizzles and refunds its chakra and cooldown.

The seal reaches for the nearest tailed beast within 100 blocks that is at 15% of its health or less (not a jinchuriki's transformation, and not already locked). If there's none, it's refunded ("no beast").
The beast's health is locked where it is: it can neither be hurt nor hurt anyone, stops moving and targeting, and is held in place.
The sealer has 60 seconds to right-click the player who is to hold it (the host). If no host is chosen in time, the hold slips (with no cooldown).
Once a host is chosen, beast and host are held fast and a thick red stream of chakra runs from the beast to the host.
The seal fills only while the sealer keeps the host in their sights: within a narrow cone of the crosshair (wider up close), with line of sight. It takes 20 seconds of keeping the host in sight to fill. A red percentage is shown to every player within 150 blocks.
At 100%, the beast vanishes in a huge burst of smoke and the host becomes its jinchuriki, earning that beast's jinchuriki advancement (a challenge advancement announced in chat).
If the host or sealer dies or disconnects first, it fails ("the seal failed") and the beast fights on.
Success or failure (once a host was chosen), the seal can't be done again for 30 minutes.

"<beast> has been sealed inside you." plays with a wither spawn sound.
You are given the Jinchuriki release item. If you ever lose a release item, it comes back to you: into your inventory, or onto the ground if that's full, where only you can pick it up.
All beast progress starts at zero.