Cause for Madness

Cause for Madness is the nineteenth chapter of the Owari no Seraph manga.

Short Summary
Shinoa Squad is out in the city (presumably Shinjuku), and Yoichi manifests his demon, Gekkōin, to kill three nearby horsemen. Shinoa and Mitsuba explain the differences between demons that manifest and those that possess. Yu attempts to learn how to use his demon before Kimizuki. He cuts his hand, ordering Asuramaru to drink his blood. The squad prepares for battle a berserk Yu, but Yu faints.

Kimizuki asks the squad about telling Yu about happened to Yu during the vampire attack, and Shinoa agrees to tell Yu everything when he wakes up.

In Sanguinem, Mika is in pain and desperately thirsty for human blood.

Long Summary
In the ruined city of Shinjuku (presumably), Yoichi scouts for monsters. Spying three horsemen, Yoichi manifests his demon, Gekkōin, and eliminates all three at once. Yoichi had such a high aptitude for controlling gear that he was able to do a manifestation without any training. He says that he and his demon talk when he goes to sleep, and manifesting it happened naturally. Yu says his demon, Asuramaru, only comes out when trying to take over Yu's body.

Shinoa and Mitsuba agree that they are far enough away from civilization to avoid any problems if anyone goes mad, and everyone awkwardly looks at Yu.

Mitsuba and Shinoa explain that a soldier must acclimate to the gear slowly or else the demon will take over. This usually takes half a year, but the boys appear to be ready. Shinoa says that Yu and Kimizuki most likely have aggressive and violent disobedient demons, which will most likely be possession times. They will be suitable for melee fighting. Manifested demons, which Shinoa, Mitsuba, and Yoichi use, vanish and appear at will.

Yu and Mitsuba spar, and Mitsuba manifests her demon, Tenjiryū, from a distance. Manifestation-types use special abilities. However, using the ability leaves the bearer vulnerable. Without someone able to defend the bearer against melee attacks, this is extremely risky in battle. Each demon manifests best a certain range. Yoichi's Gekkōin is long-range, Shinoa's Shikama Dōji is mid-range, and Mitsuba's Tenjiryū is close-to-mid range.

In order to become close with their demons, Yu and Kimizuki must cut themselves and order their demons to drink their blood.

Yu goes first. The squad prepares for battle since Yu may go berserk at any moment, but he faints. It may be another 20 hours before he fuses with his demon, and he may go berserk at any time. Kimizuki asks about informing Yu about what happened on the battlefield. During their interrogation, Yoichi and Kimizuki only told the higher-ups that they did not know anything and were just following Shinoa's orders. If they are genuinely friends and family, Kimizuki wants to tell Yu the truth. If that is only a front, then he will say nothing because he needs the money, but he will only work for the money. They agree to divulge the truth to Yu when he wakes up.

In Sanguinem, as children play nearby, Mika sits on the streets, sweating and gasping in pain as he fights his thirst for human blood. He says Yu's name and mutters that it hurts.