This is where the Akatsuki members seal away the king of hell statue that the Leader summons. The pair that captures the biju brings it to the base and summons astral projections of everyone else to extract the biju. This process takes 3 days to complete and takes a lot of energy out of each member. During the sealing process the Jinchuurik is surrounded by a giant blue ball of chakra witch extracts the biju into the king of hell statue. Each eye represents a biju, The eyes with pupils represent captured bijus. It was stated previously that the Kyubi has to be sealed last because the other biju balance the Kyuubi's power. If it is not sealed last the king of hell statue will crack and be destroyed.
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((Note: For enemies looking to get in here and interupt an extraction, you would first need to get past the traps at the Akatsuki Base.))