Omen (前兆, Zenchō) is the 4th episode of Muhyo & Roji's Bureau of Supernatural Investigation anime series.
Muhyo and Roji arrive at the Magical Law Association so Roji can take the promotion exam, and for whatever reason, Nana has come along with them. They're greeted by Muhyo's former classmate, Yoichi, who mentions a name that seems to strike fear into the hearts of those who hear it. The gang's concerns become reality when a spirit appears during the exam briefing...
Nana decides to follow Muhyo and Roji and enters the portal to the Magical Law Association. There they get greeted by Yoichi Himukai, who tells Muhyo didn't tell him he will be bringing busty beauty like her, but that only creeps out Nana. As they walk Roji explains they are somewhere in Azumino mountains. Muhyo and Yoichi heads out, and Muhyo tells Roji to stay with Nana until he hears the exam registration bell. Yoichi realizes that Muhyo still haven't told Roji about Enchu. Nana goes sightseeing and takes pictures of everything. She sees a building with MLS and Roji explains that's Magic Law School, and that Muhyo and Yoichi studied there as kids. Hearing some kids getting scared that Enchu may come, now that Muhyo is there, Roji realizes Enchu is Muhyo's friend that went to the dark side.
Yoichi tells Muhyo that two executors had died from evil spirits since the beginning of the month, but Muhyo tells him he wasn't there for that. Yoichi then he has been looking for Enchu and hears that he is in Shin'etsu region.
Roji and Nana go into the Magical Law Library and Roji goes to look for the Magic Law Journal issues that featured Muhyo, but realizes they are gone. Roji then sees a man with white hair passing by and notices the scars on his neck. Roji hears the exam registration bell and heads out. Nana notices a burning paper with Muhyo face coming from the mysterious man.
During the exam registration, Nana observes from above and is approached by Yoichi, but he seems weird and multiple mouths that laugh appear on him, scaring Nana and making her scream. The examiner along with Muhyo and Roji quickly head upstairs, but see Yoichi being normal. But as Nana touches him and the examiner touches her, Roji notices mouths appearing on their necks. Muhyo tells him to keep quiet and to not touch them, otherwise it will transfer to him too. The students keep shaking hands with Yoichi, which makes the spirit spread among many people. Muhyo has started his sentence secretly and Roji decides to check the law book to see what's the sentence, but as he was focused on the book, Nana touches him and infects him too. Roji then notices mouths appearing on Yoichi and him and starts to scream. As other notice them too, they start to panic and run around touching and infecting other people. Muhyo had summoned a Spirit Striker, who managed to find the original spirit and kills it. The Spirit Striker then tries to attack the mysterious man, but he easily defeats it.
As the exam is postponed, Roji blaming himself for getting in Muhyo's way and decides to leave. Yoichi tells Muhyo he will go find him. As he find him, Roji explains his reasons and states he doesn't have talent. Yoichi then decides to tell him about Enchu.