Seal Door

The Seal Door is the mystical gate that Daimaou and the Youkai were sealed behind.

History
Millennia ago, three three holy men, the original forms of the Sanshinsho, developed the shinobi spell that trapped Daimaou in the Seal Door after Daimaou attacked the humans with his Youkai minions. Nurarihyon suffered the same fate years later at the hands of Sasuke Sarutobi, Saizou Kirigakure, Seikai Miyoshi, Jiraiya, and Tsuruhime, the ancestors of the Kakurangers.

Centuries later, the modern day Sasuke and Saizou were tricked by Kappa into opening the door and releasing the sealed Youkai, although Daimaou was unable to come through.

Some time later, Gashadokuro, Daimaous son, set up a ritual to bring his father into the human world by turning fifteen children into stone. This caused the the Gate to appear in the city this was taking place, although Daimaou wouldn't be able to exit for a month. This gave the Kakurangers enough time to gather enough power to destroy the Door. It was too late, however, and Daimaou was still able to enter the human world.

Eventually, the Kakurangers were able to use their Doron Changers to seal the Youkai behind the door once more.