Shadow Realm

In attempt to be able to gain access to the Naraka Realm used by Ryuga's idol Raido, Ryuga tried to get here using his Kamui instead sending him to the Shadow Realm. Ryuga didn't know that in order to get there Raido uses is Siddha, Ryuga didn't figure this out until he did his own research. Since, Ryuga failed he did his studies onto the Shadow Realm he learned that the souls he trap there, unlike Raido's Naraka Realm can be used in the Summoning: Impure World Reincarnation Technique. In order to be able to do this Ryuga sends someone or goes himself to the realm while bringing a Scroll to put the souls on, comes back to the "Pure" World uses the soul in a Reincarnation. Ryuga can even send regular souls here and use them as sacrifices of the Technique.

Souls Captured

 * Kyoya Uchiha