Centuries ago, under the leadership of Daimaou, the Youkai Army Corps launched a campaign of terrorism against humans until Daimaou was sealed away by three holy men.
With Daimaou gone, the Youkai were scattered until they were united by Nurahiyon, who led them in another series attacks until they were sealed away 400 years ago by the ancestors of the Kakurangers.
In the present day, the Youkai emerged again with Gashadokuro serving as their acting leader until they could revive Daimaou. Though Gashadokuro was defeated by the Kakurangers, before he died he unsealed Daimaou, who retook leadership of the Youkai Army Corps from then on.
After the Daimaou was defeated and sealed again by the Kakurangers, the Youkai Army Corps was no more.