The content below is entirely editable.
A prequel to the anime series Un-Go, this OVA elaborates on the pasts of Yuuki, Inga and Bettenou.
Yuuki Shinjurou reflects on his life.
As a child, his parents left him, so he was raised by various strangers instead. He decided to try and find a way to help others become happy. He first tried to throw himself into swimming competitions, as he had a knack for it, but soon quit after he determined that it wouldn't help anyone else. Then he tried displaying films around the country, but he encountered several hardships and eventually became broke. While sitting in a market one day he ended up meeting the members of a band called "Singing on the Battlefield," and traveled around the country with them.
The scene shifts back to the present, where Yuuki and Inga are summoned by Public Prosecutor Izumi and her representative in the police (Seigan) to solve a strange case: members of a cult started by Yuki's former friend Ono, worshipping a being named "Bettenou." Every day, the cult holds a ritual to sacrifice one "unbeliever" who thinks of quitting the cult. A police informant managed to sneak a camera into one of the meetings, and Bettenou killed one of the unbelievers, but the camera didn't show who or what caused it, so the police cannot intervene. The informer soon quit the police and joined the cult as a member after that. On top of that, Ono seems to have a private section of the JSDF as his personal bodyguard unit to keep uniformed police out. Yuuki decides to investigate, as he knows that Ono can't be the cult leader, because he killed him in the past.
The scene shifts back to the past, where Yuuki and the members of "Singing on the Battlefield" are resting and talking about topics to each other. The next day, they end up driving straight into the middle of a large battle, where the car crashes into a cave. Yuuki manages to get the band out of the car before a gas leak leads to an explosion. The band survives, but Yuuki's throat is impaled on a large rock spike in the cave. However, he slowly pulls himself off of the spike and appears to heal with a strange glowing light.
In the present, Yuuki visits the bandaged head of the cult and accuses him of being Serada, the only man who survived that night in the cave. However, the unraveling of the bandages reveals the face of a scarred-yet-alive Ono. Yuuki then gets punched by one of Ono's followers, earning him a quick trip to the hospital. Yuuki talks to the doctor about the dental records of both Ono and Serada, and though they seem different, the doctor insists they are the same. Soon after that, Izumi takes Yuuki and Inga to a computer store to view a clip of four of the band members being tortured and then executed by enemy forces, but all Yuuki can see is a blurry picture of a blue sky. Izumi wonders out loud how some people can see the gruesome video while others see nothing but the blue sky.
The next day, Yuuki encounters Serada in a public park, where Serada tells Yuuki that he plans to expose Ono and needs his help to do it.
Going back to the cave scene, Yuuki encounters Inga for the first time as a disembodied spirit that possesses his body and uses him to eat the souls of the members of "Singing on the Battlefield" while they wonder where Serada went. Inga describes it as eating the "screams" of humans that are stored within their bodies. Inga eats them one-by-one, leaving Yuuko for last.
In the present, the Bettenou cult is in anguish as they claim that Ono has been murdered, and Yuuki is the prime suspect. Seigan claims to have seen him throw a molotov cocktail that burned Ono alive earlier that day. As the cultists try and break past the police perimeter, Yuuki and Inga escape in the confusion.
Switching back to the flashback, Yuuko tries to plead with Inga for mercy, but when Inga plans to devour her anyway, she picks up a shard of a broken guitar and stabs herself with it.
In the present, Izumi takes Yuuki and Inga to a small sushi stand, and says that he needs to find the real culprit or otherwise she will have no choice but to arrest him. She also provides evidence that Serada used to be a member of the SDF but soon disappeared. However, Serada himself shows up and uses Bettenou to scare everyone into thinking that there is a bombing raid going on, then uses the distraction to talk to Yuuki face-to-face. He claims that Bettenou is a god created by the thoughts and dreams of old Japanese warriors that carried them into battle, but then were left behind when those warriors fell. Apparently, Serada discovered Bettenou around the same time that Yuuki found Inga. Yuuki asks Serada why not use Bettenou's powers for good, and he responds that it is not his place to help everyone out. If he did, someone else would fall behind.
Serada then sics Bettenou on Yuuki, causing him to bleed from the shoulder. Yuuki ends up flashing back to the point when Yuuko stabbed herself with the broken guitar. Inga managed to heal her body, but the woman known as Yuuko died from the stomach wound before Inga could possess her. Yuuki then tries to strike a deal with Inga, that he will give her all the souls she wants from the many people who lie if she can do it without actually killing another person, and in return Yuuki pledges to let Inga peek into his own soul when she is done. Inga decides to accept it. This transitions into the present, where Yuuki demands that Inga peek into his own mind to break through Bettenou's manipulation of his senses. Though he will lose his chance to determine what truly lies in his soul, Inga makes Yuuki see the truth in front of him, breaking Bettenou's spell.
Apparently, Bettenou herself doesn't kill people, but makes the target think she is, to the point where they rend their own flesh until they die. Realizing this, Yuuki is able to stand on his own feet and face Serada. But Serada takes out a pistol and mockingly asks Yuuki if he thinks it is an illusion. At that point, the policeman Seigan shows up to arrest them both, and Serada orders Bettenou to make Seigan shoot and kill "the true criminal." Seigan fires and hits Serada in the chest, as he was the "true" criminal in that situation.
The case is considered closed as Bettenou disappears from sight. However, Rinroku Kaishou informs Yuuki that his real identity will forever be known as the one who killed the cult leader Ono and was later shot by police while resisting arrest, as the real explanation is considered too outlandish for the public. As a token of gratitude, Izumi hands the detective a brand new identity, the name and face he is known by today (and throughout the series): Yuuki Shinjurou. Izumi offers to find him some public housing, but Yuuki declines the offer and instead decides to live in the ruins of post-war Tokyo.
In the epilogue, Kaishou manages to catch a glimpse of Bettenou herself through a security camera before that camera suddenly dies.