Shadow Realm (Arashi Mitarashi)

The Shadow Realm is a tool used by Arashi Mitarashi and forms the backbone of his dark release techniques. Every Dark release technique used seals chakra or matter into the shadow realm.

As Kosaru explained being inside the shadow realm is like being inside Arashi's smog technique, suffocating. But in addition the gravity in the realm is some ten times as much as on earth. Contrictions apply when inside, even Arashi, its wielder, does not know where he will end up after using Eject, instead he requires Kosaru's Sarugan to guide him to a desired location.

As such the shadow realm can be considered a kind of Kamui Dimension.