The Onisu were one of the first creations of Daigotsu, when he first became powerful in the Shadowlands. They were the result of an alliance he formed with the enigmatic Tsuno. Drawing upon their aid and the aid of Tsuno Nintai, Shokansuru, and Omoni, Daigotsu created a new breed of oni from the raw stuff of Yume-do, the Realm of Dreams. 
Early Experiments Edit
The first process of binding demons to nightmare was ineffective, as it was proved with Tamayu no Oni, the demon the Tsuno helped the Shimizu family to summon in the 9th century. At the worst possible moment the oni had raged out of control. The experiment taught that simply summoning a demon in the mortal realm was not enough. A powerful magical anchor was needed in Jigoku, a shugenja in the Realm of Evil. 
Onisu were a blend of oni and baku, literally the stuff of nightmares from Yume-do. These beasts were created with the aid of the Tsuno and magic stolen from imprisoned Morito Tokei,  who was tortured by The Maw in the depths of the Realm of Evil. To mitigate the pain, Tokei willed himself into unconsciousness. However, his doing so created a small opening between Spirit Realms that allowed a stream of power to flow from the very depths of Jigoku into the Realm of Dreams. 
Each of the Onisu represented the worst aspects of one of the Great Clans.  Created from the dreams of samurai, they embodied their greatest fears and most hated stereotypes. They would feed off of the basest impulses in a samurai's heart and each time the samurai failed their nightmares would become stronger.
Daigotsu's spirit was able to posess an onisu's body, making it stronger and bigger. Daigotsu was, for example, posessing Kyofu when it killed Kyoso no Oni.  He also did the same posessing Fushin when it attacked and killed Emperor Toturi I.
The onisu were effectively immortal, as if they were slain they merely return to Yume-do where they remained in stasis until they were retrieved again by Daigotsu, in a long and extremely taxing ritual. 
The Onisu Edit
Though they lacked the raw physical power of some of the other creatures that had crawled out of the Festering Pit of Fu Leng, their power to feed off of the sins of mortals and keen intellects made them far deadlier foes. Of all of them Hakai and Kyofu were the most powerful as death and fear were quite common in day to day Rokugan. In contrast Settozai and Muchitsujo were the weaker as samurai were trained from a young age to resist their weaknesses.
- Fushin, Onisu of Betrayal, Nightmare of the Scorpion Clan.
- Hakai, Onisu of Death, Nightmare of the Phoenix Clan.
- Kanashimi, Onisu of Regret, Nightmare of the Dragon Clan.
- Kyofu, Onisu of Fear, Nightmare of the Crab Clan.
- Muchitsujo, Onisu of Chaos, Nightmare of the Unicorn Clan.
- Nikushimi, Onisu of Hatred, Nightmare of the Lion Clan.
- Settozai, Onisu of Larceny, Nightmare of the Mantis Clan.
- Yokubo, Onisu of Desire, Nightmare of the Crane Clan.
The Onisu Unleashed Edit
The Onisu made several appearances in Rokugan, but most notably in 1159 they were all unleashed upon the Empire at the same time when Daigotsu wished to avenge the death of his bodyguard Goju Kyoden. They were sent to infiltrate the homes of the Four Winds and kill as many people as they could before they themselves perished. Kanashimi died to Kaelung's ono in the ruins of Kyuden Tonbo, the home of Toturi Sezaru. Yokubo and Hakai were killed in Kyuden Seppun, through the coordinated efforts of Shiba Mirabu, Megumi, Shiba Aikune and Doji Okakura. In Ryoko Owari, Hantei Naseru's headquarter, Muchitsujo was beheaded by Bayushi Shixiang and Fushin was burnt by Bayushi Kwanchai. In the Shogun Kaneka's camp, Settozai was struck down by the poet and Returned spirit Rezan, while Nikushimi was destroyed by the unified attacks of many Akodo and Matsu who were inspired by Matsu Hyun's song. Below the Kaiu Wall Kyofu was torn apart by the nezumi Yoee'trr, who had been strengthtened by the Kami of air summoned by Asako Hirariko.
Kuroda and Kyofu Edit
Kyofu became a distinct and singular Onisu. After the death of all of the Onisu in their vengenful raids, Daigotsu decided to not take them back and took another way with the empty shell of Kyofu. Daigotsu summoned the undead Hida Kuroda and put him on Omoni's hands even against the Crab's will. The half-goblin combined the undead with the Onisu in a single body, and Kyofu was again alive, but never the same as he was before. 
Betraying Daigotsu Edit
when in 1165 the Bloodspeaker, Iuchiban, defied Daigotsu, the Onisu remained apart from this war in the Shadowlands. Hakai believed they had nothing to gain until a winner presented himself.  Instead, the Onisu's leader decided to side with the Oni Lord Akuma no Oni,  while Fushin aligned with the Oni Lord known as the Maw, and Kanashimi followed suit.  In 1166, Hakai was banned back to Yume-Do, as a result of his failed attempt to control Naka Tokei's soul.  Kanashimi was killed by Isawa Sezaru after failing to make him regret anything.  Unlike the other Onisu, Kyofu chose Daigotsu's side and then began a path towards its later redemption in 1169 Kyofu's Last March. 
Onisu's Fate Edit
- ↑ 1.0 1.1 Nightmares, Part I, by Rich Wulf
- ↑ Secrets of the Lion, p. 90
- ↑ 3.0 3.1 Fortunes & Winds, p. 35
- ↑ Creatures of Rokugan: Third Edition, p. 147
- ↑ Specter of Yesterday (Imperial Histories), by Rich Wulf
- ↑ 6.0 6.1 6.2 Nightmares, Part II, by Shawn Carman
- ↑ 7.0 7.1 A Moment of Regret, by Shawn Carman and Rich Wulf
- ↑ Finding the Balance, by Shawn Carman
- ↑ Imperial Histories 2, pp. 220, 222
- ↑ Fate of the Grand Master, by Rich Wulf
- ↑ Oaths, by Shawn Carman and Rusty Priske
- ↑ Imperial Histories 2, p. 217
- Four Winds, pp. 79-81.