Not to be confused with Yokai Realms, Dark Realms are areas in missions infested by Yokai. On the mini-map they appear as grey clouds and on screen they can be seen from the outside as shimmering grey and black auras. While inside a Dark Realm, colors will be dimmed and greyed and the same black-grey shimmer will be present on screen.
While inside a Dark Realm, Yokai defense and damage are boosted and the player's Ki recovery is greatly diminished, which can be counteracted with several of the skills in the Shiftling skill tree as well as by raising Dark/Other realm resistances. Thus, it is advisable to keep Ki recovery-boosting items on hand when entering a Dark Realm to avoid running out of Ki while inside. Chests in Dark Realms cannot be opened until the Dark Realm has been dispelled.
Boss Dark Realms
Yokai bosses will plunge the boss arena into a Dark Realm shortly after their Ki runs out. These special Dark Realms will only disappear when the boss lifts them - a process which can be expedited by forcing them to run out of Ki while inside the Realm.
Dispelling Dark Realms
With the exception of the Dark Realms created by bosses, Dark Realms can only be dispelled by killing the host Yokai, which will be clearly indicated by the aura of red flowers on the ground surrounding it. A good strategy to deal with Dark Realms is to enter the realm, use Sneak Thief and Catwalking jutsus and searching for the host. By doing this you ensure that you only have to deal with one strengthened Yokai inside the realm, leaving the rest more vulnerable once it has been dispelled.