Eight Trigrams Sealing Style

The Eight Trigrams Sealing Style, consisting of two Four Symbols Seals, was used by Minato to help Naruto Uzumaki access the chakra of the Nine-Tailed Demon Fox sealed within him. This seal weakens over time. To strengthen the seal again when it gets too weak, Minato drew a key on the abdomen of the scroll toad Gerotora.

What is noteworthy about this jutsu is how it is possible to implant the chakra and personalities of other people inside of it.

When Orochimaru used the Five Elements Seal on Naruto, this created an imbalance due to an odd-numbered seal being placed over an even-numbered one. As a result, Naruto not only lost access to the Nine-Tails' chakra, but also had difficulty controlling his own, until Jiraiya removed it.

Noted Jinchūriki Killer Bee has remarked that this seal is high-quality and more durable compared to the Iron Armor Seal that holds the Eight-Tailed Giant Ox. As part of Naruto's effort to control the Nine-Tailed Demon Fox, he has undone the seal using the key given to him by Gerotora.