The Spirit Gate (「幽門扉」?; Yū monpi; lit. "secluded gate", "spirit door") is a sacred portal and is used only a few times by a few characters. The gate takes whoever passes through it to another place and time. It is said that needlessly opening it will engulf one in a dark, sinister air. In actuality, it appears to be a sort of time travel device (although it only has one known destination). Only Ishaku and Issun can open it with Denkomaru.
Amaterasu and Issun explore Inner Yoshpet to find the Spirit Gate, which Lika is said to have gone through. When they find the gate, Issun opens it so they can proceed. Oki shows up, claiming that Kutone lead him there. He decides to use the gate to defeat the "monsters of misfortune" and make Kutone glow silver. Issun warns him that he might get more than he can handle, to which Oki hopes so. Amaterasu follows him through the doorway, the Spirit Gate closing up behind her.
On the other side of the gate, Amaterasu, Issun, and Oki find themselves in a familiar place: Kamiki Village. What they do not know, and will later find out, is that this Kamiki is from one hundred years ago. Amaterasu and Issun then set out to fulfill the legend of Nagi, save Lika, and defeat True Orochi.
After saving Lika from True Orochi, Amaterasu and the others go through the Spirit Gate to go back home. They take Lika to Laochi Lake so she can perform the Volcanic Incantation. However, Amaterasu discovers that she must first defeat the twin demons Lechku & Nechku before Lika is able to perform the holy prayer. She enters Wawku Shrine and later confronts the Silver Demon Nechku. Before Amaterasu fights the demon, she is joined up with Shiranui, her past incarnation.
Shiranui had used the Spirit Gate to help her future self. Before Amaterasu is able to finish off Nechku, the Gold Demon Lechku crashes in, Oki fighting him. Oki tries to kill the demons, but they freeze time. As they prepare to kill Oki, Shiranui breaks free from the spell and pushes Oki out of the way, taking the blow himself. The demons escape since Oki chose to save both divine wolves from a falling ice tree instead of finishing them off (the demons).
When they re-enter Wawku Shrine, Oki chooses to defend Shiranui while Amaterasu finds a way to the other altar, where the demons escaped to. Amaterasu finds the altar, along with Oki, and they join together to fight the demons. After a long battle with the demons, Amaterasu and Oki were able to defeat them. They later join up with Shiranui, who, upon seeing Oki's glowing sword Kutone, gathers enough strength to pass through the Spirit Gate with Ishaku. This is the last time the Spirit Gate is used and/or mentioned. The gate can still be visited, but Issun does not want to open it because it has already served its purpose.
In Ōkamiden, the Spirit Gate can be seen behind Konohana in the past. However, it cannot be opened.