The Shikiouji (or Shiki-Ouji) is an exceptionally powerful type of Shikigami that could only be summoned as a servant by the most elite of those that practiced the mystical arts of Yin and Yang. It could be used to scare away demons that cause sickness and to ward off disasters to its master. The Shikiouji's basic nature is said to be very close to that of an Oni and is thus very ferocious, making it very dangerous for average mystics to attempt to summon it.
They first appear during the Manikin massacre in random encounters in the Mifunashiro and Asakusa areas. Shiki-Ouji can also be found within the Mantra HQ and can be surmised to be a follower of Yosuga.
"A powerful shikigami that can be summoned by certain onmyodo. It can cause harm to others or cure illness, but its ordinary temperament is quite vicious."
—Devil Summoner: Soul Hackers 3DS Compendium
Shiki-Ouji reappears a demon exclusive to the 3DS remake, available after Nemechi evolves into the leg form (female growth path), and costs 300 D-Souls. His artwork is based on his appearance from Shin Megami Tensei III: Nocturne.
"A powerful shikigami of Izanagi-style, an ancient sect of Onmyoudou in what is now Kochi Prefecture. In Izanagi-style prayer songs, a priestess named Amenaka-hime was apprenticed to the Indian god King Izanagi and began training in the ritual arts. It is said that Shiki-Ouji spirits were bound into paper and could be used to protect against illness and inflict curses."
—Devil Survivor 2 Record Breaker Compendium
Shiki-Ouji is summoned by the party on Thursday of the Triangulum Arc to aid them against Arcturus. Shiki-Ouji will only obey those he believes are worthy of being his Tayuu however, leading to a battle to determine the protagonists worth. He creates three copies of himself to aid him in battle, with two teleporting to the other side of the party. Each Shiki-Ouji is joined by two Shikigami. During battle, if any one Shiki-Ouji party has Shikigami present, a Shikigami can sacrifice itself to resurrect a defeated Shiki-Ouji and its two Shikigami.
After the battle he accepts the protagonist as his Tayuu master. Yamato then takes Shiki-Ouji and harnesses his power for an app on the protagonists phone, allowing him to take damage from Arcturus' Plough of Death attack in place of his friends. The app only works on humans however and all demons will keep their weakness, likewise the protagonist cannot remove his own weakness. When Miyako Hotsuin joins the battle against Arcturus he can use the Soul Bind app again to take the damage she would take.