A terrible war has ravaged the land, and now, fueled by the blood of numerous fallen warriors the Yoma, demons from hell, emerge once more. A skilled ninja seeks to end the bloodshed these demons inflict upon humanity, but to do this he must fight against his undead former best friend and fellow ninja who was killed in battle and has been resurrected to serve the Yoma. (Source: ANN)

In the five hundred years since Earth's environment was destroyed and the planet came to be known as Terra, humans have created a society in space that is entirely logical. Supercomputers control the government, babies are grown in artificial wombs and assigned parents randomly, and at age 14, children take an Adulthood Exam. Humanity's greatest enemy is the Mu—humans who have developed into espers. When Jomy Marquis Shin's birthday arrives and the time comes for him to take his Adulthood Exam, he is shocked to learn that all of his childhood memories are going to be erased. Suddenly, he hears the voice of Soldier Blue, the leader of the Mu, calling out to him to hold onto his memories. Jomy makes his escape on a Mu ship and is shocked to learn that he himself is an esper and that the government has sentenced him to death. Nearing the end of his life, Soldier Blue transfers his memories to Jomy and names him the next leader of the Mu. Now, Jomy has a choice: keep the Mu in hiding, or declare war on humanity to realize their dream of returning to Terra.

Half a century after a devastating war that brought Japan on the brink of destruction, a centralized network named Sound Health Everlasting Long Life (SHELL) has become the basis of the new society. Thanks to cutting-edge research on nanomachines and medical treatment, people are guaranteed a life free of diseases, but they are expected to work 19 hours a day in return. Moreover, when someone disconnects from the SHELL system, an extremely rare phenomenon called Human Lost takes place, transforming humans into monsters—Lost—that need to be destroyed, lest society will collapse for good. However, in this society where the fear of pain and death is absent, antisocial behavior is on the rise. Factory worker Takeichi plans to besiege the Ministry of Interior to protest against his inhumane living conditions and manages to convince his friend, the unknown painter Youzou Ooba, to join his cause. But when their suicide operation inevitably fails, Takeichi is left with a body beyond repair and mutates into a Lost, with Youzou immediately following suit. In the ensuing fight, a member of the dispatch team, Yoshiko Hiiragi, uses her ability to detect the Lost and discovers that Youzou has the unique capacity to return to human form. As the third person who survived after becoming a Lost unit, Youzou soon joins Yoshiko in investigating the recent outburst of Human Lost phenomena that threaten the last chances civilization has to be reborn.

Onmyouji tells the story of renowned onmyouji Abe no Seimei, who meets and befriends the straightforward court noble Minamoto no Hiromasa. Together, they deal with strange cases in the Heian capital surrounding demons and curses.